Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minutefssync.dll is a Kaspersky Anti-Virus application file, not a normal Windows system component. If Windows reports that fssync.dll is missing, was not found, or could not be loaded, repair the Kaspersky installation that owns it rather than downloading an isolated DLL.
Start with this diagnostic checklist
Before changing Windows files, answer these questions:
-
Which program triggers the error?
Does it appear when Kaspersky starts, when Windows boots, or when another application opens? -
When did it begin?
Note whether the problem followed a Kaspersky update, incomplete uninstall, cleanup utility, sudden shutdown, or antivirus detection.Free tools Windows power users keep installed
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Is Kaspersky still installed?
Check Settings → Apps → Installed apps in Windows 11 or Settings → Apps → Apps & features in Windows 10. -
Where is the file, if it exists?
A genuine copy should normally be inside a Kaspersky installation directory, notC:WindowsSystem32,C:WindowsSysWOW64, a temporary folder, or a random user folder. -
Is the affected software 32-bit or 64-bit?
Historical records include 32-bit Kaspersky-era copies, but that does not prove every build has the same architecture. Do not choose a replacement DLL based only on its filename.
These checks usually identify whether you have a damaged Kaspersky installation, a quarantine event, or a stale startup reference.
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fssync.dll has the internal name FSSync.DLL and historical file metadata identifies Kaspersky Lab as its company and Kaspersky Anti-Virus as its product. It is an application module associated with Kaspersky software.
Historical references connect the file with older Kaspersky Anti-Virus Personal and Workstation products, Kaspersky Anti-Virus 7.0-era software, Kaspersky Security Center components, and Kaspersky Security for Windows Server. The exact public function of the DLL is not documented well enough to identify a specific feature safely.
It is not a Microsoft Windows component. It should not normally be copied into:
C:WindowsSystem32C:WindowsSysWOW64- The folder of an unrelated application
- A temporary download directory
Older records show multiple file versions and builds, so a file with the right name can still be the wrong file for your installation. A DLL copied from another computer or another Kaspersky product may have incompatible exports, dependencies, or architecture.
The fastest safe fix: repair or reinstall Kaspersky
For most users, a damaged or incomplete Kaspersky installation is the most likely cause. This can happen after an interrupted update, failed uninstall, cleanup operation, disk problem, or sudden shutdown.
Step 1: Check whether Kaspersky is installed
- Press Windows + I.
- Select Apps.
- Select Installed apps on Windows 11, or Apps & features on Windows 10.
- Search for the installed Kaspersky product.
- Select the three-dot menu beside it in Windows 11, or select the product in Windows 10.
- Choose Uninstall, Modify, or the available maintenance option.
If a Kaspersky maintenance wizard opens, choose Repair if it is offered. Not every Kaspersky product exposes the same repair controls.
- Let the wizard finish.
- Restart Windows.
- Test the action that previously produced the error.
If the error is gone, the installation was repaired. If repair is unavailable or fails, continue with a clean reinstall.
Step 2: Reinstall from Kaspersky
- Save your work and close running programs.
- Remove the installed Kaspersky product through Settings → Apps.
- Follow the Kaspersky removal wizard rather than deleting its folders manually.
- Restart Windows.
- Open a browser and go to Kaspersky’s official website.
- Use its official Windows downloads page to select the product you actually use.
- Download the installer directly from Kaspersky.
- Before running it, confirm that the download is from Kaspersky and that Windows does not report an invalid or untrusted signature.
- Run the installer as an administrator if Windows requests permission.
- Complete setup and restart Windows again.
Do not install an older Kaspersky product merely because its historical records mention fssync.dll. Use the supported product for your subscription or the exact enterprise package supplied by your organization.
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For an enterprise installation, contact the administrator responsible for Kaspersky Security Center or the server product. Use the installer matching the exact product and version. Some Kaspersky installers support a repair mode using a command such as:
--install-mode=repair
This is not a universal command for every Kaspersky product. Do not add it to an arbitrary installer unless the product’s documentation confirms that it supports the option.
Check Kaspersky Quarantine before restoring anything
Kaspersky may have quarantined or deleted the file after detecting a damaged file, a false positive, or suspicious activity. A missing file alone does not prove that the detection was wrong.
On a local Kaspersky installation
- Open the Kaspersky application.
- Open Security, More tools, or the section containing detection history.
- Open Quarantine or Backup.
- Find the detection associated with
fssync.dll. - Inspect the original path and detection details.
- Confirm that the original path was inside the Kaspersky installation directory.
- Check whether the installed Kaspersky product still requires the file.
Restore the file only when its original path, product ownership, digital signature, and current detection status are consistent. Then update Kaspersky and run a scan.
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In Kaspersky Security Center
A managed installation may place the object in a central repository rather than on the local computer.
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- Open the Kaspersky Security Center administration console.
- Open Repositories.
- Select Quarantine or Backup.
- Locate the file and review its original path and detection information.
- Restore it only after the administrator confirms that it belongs to the managed Kaspersky installation.
- Run an update and scan after restoration.
Never restore a file simply because its name is fssync.dll. Malware can use the same filename.
Verify the file path and digital signature
If the file exists, inspect it before taking action.
- Press Windows + E to open File Explorer.
- Locate the file from the error message or search only within known Kaspersky folders.
- Right-click the file and choose Properties.
- On the General tab, note the full location.
- Open the Details tab and check the internal name, company, and product information.
- Open Digital Signatures if that tab is present.
- Select the signer and choose Details.
- Confirm that Windows reports the signature as valid.
A valid signature is useful evidence, but it is not the only check. A signed file in the wrong directory may still be unrelated to the installation that is failing.
Treat these findings as suspicious:
- The file is in a temporary directory.
- The file is in a user profile folder without a clear reason.
- The file has no valid Kaspersky signature.
- Its product details identify unrelated software.
- Multiple unrelated DLLs are missing.
- The issue appeared after suspicious downloads or account activity.
In those cases, run a full or offline malware scan with a reputable security product before restoring or replacing anything.
Find a leftover startup entry if Kaspersky was removed
If the error appears at every boot, but Kaspersky is no longer installed, Windows may be trying to start an orphaned service, scheduled task, shortcut, or enterprise agent.
Do not immediately delete every entry that mentions fssync.dll. First identify what launches it.
Check Startup apps
- Press Ctrl + Shift + Esc.
- Select Startup apps.
- Look for an old Kaspersky entry.
- Right-click it and choose Open file location if available.
- Record the publisher and path.
- Disable the entry temporarily.
- Restart Windows.
If the boot error disappears, the disabled entry is relevant. Remove the old Kaspersky product using its supported uninstaller or reinstall the same product and remove it cleanly. Do not delete an entry belonging to a current security product without confirming its ownership.
Check Services
- Press Windows + R.
- Type:
services.msc
- Press Enter.
- Look for a Kaspersky service or an enterprise Network Agent.
- Open Properties and record the service name and executable path.
- Do not stop or delete it if your organization manages the computer.
- If it clearly belongs to an incomplete personal uninstall, use the Kaspersky removal procedure instead of deleting the service manually.
Check Task Scheduler
- Press Windows + R.
- Type:
taskschd.msc
- Press Enter.
- Select Task Scheduler Library.
- Review tasks with Kaspersky names or paths.
- Open a task’s Actions tab and inspect the executable path.
- Disable a clearly obsolete task temporarily, then restart Windows.
If a Kaspersky process is still expected to run, reinstalling the matching product is safer than removing its startup reference.
Do not use regsvr32 for routine fssync.dll errors
regsvr32 registers DLLs that expose a registration entry point such as DllRegisterServer. It does not copy a missing file, repair a Kaspersky installation, restore deleted dependencies, or correct a 32-bit/64-bit mismatch.
Running this command is therefore not a routine fix:
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Pick the symptom - the matching free tool is one click away.
regsvr32 fssync.dll
It may produce an error because fssync.dll is an application-support module rather than a self-registering COM component. Even if registration succeeds, it would not prove that the correct Kaspersky installation has been repaired.
Use regsvr32 only when the software vendor specifically tells you to register that exact DLL for that exact product.
Do not download fssync.dll from a DLL website
Downloading a standalone copy is risky because it may contain malware, belong to a different Kaspersky build, use the wrong architecture, or omit other damaged files. It also leaves the underlying installation problem unresolved.
Do not:
- Copy the DLL from another computer.
- Download it from a random DLL repository.
- Copy it into
System32orSysWOW64. - Replace it with a similarly named file.
- Put it in the folder of an unrelated program.
- Use a registry cleaner to “repair” the reference.
The safe source is the official Kaspersky installer for the installed product, or the approved enterprise installation package supplied by your organization.
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There is no reliable evidence that fssync.dll itself is a Microsoft Visual C++, DirectX, or .NET runtime file. Installing one of those packages merely because the error mentions a DLL is not a sound repair method.
Install a Microsoft runtime only when the application’s error identifies a missing runtime dependency or the application’s official documentation requires it. If a Visual C++ Redistributable is required, its architecture must match the application that uses it, not necessarily the architecture of Windows.
For the same reason, changing Windows Features is not a default fix. Do not enable .NET Framework or legacy components solely to address fssync.dll.
Use SFC and DISM only for broader Windows corruption
SFC and DISM repair protected Windows components. They normally cannot restore a third-party Kaspersky DLL.
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Use them when Windows has additional symptoms, such as damaged system applications, repeated Windows component errors, failed updates, or several unrelated protected files reporting corruption.
- Open Start.
- Type Command Prompt.
- Right-click Command Prompt.
- Select Run as administrator.
- Run DISM first:
DISM.exe /Online /Cleanup-image /Restorehealth
- Wait for it to finish.
- Run System File Checker:
sfc /scannow
- Restart Windows.
- Test the failing application again.
If SFC reports that it repaired files, restart and retest. If it reports that it could not repair everything, repeat the process only as part of broader Windows troubleshooting. Do not expect it to recreate a missing Kaspersky-owned DLL.
Manually comparing DISM and SFC output can be tedious when several Windows components are involved. Outbyte PC Repair can scan for system issues and show what needs attention; its repair functions require the full version, and reinstalling Kaspersky remains the definitive fix for this application-owned DLL.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Drivers are usually unrelated
A graphics, chipset, storage, or network driver is not a normal solution for a Kaspersky fssync.dll error. Update drivers only when Device Manager reports a device problem or the error began with wider hardware instability.
To inspect devices:
- Right-click Start.
- Select Device Manager.
- Expand categories with warning icons.
- Right-click the affected device.
- Select Properties.
- Review the General and Driver tabs.
- Use Update driver only for the device involved.
- Restart Windows and test again.
Do not replace a driver because a DLL website recommends it. If several devices have old or mismatched drivers, manually identifying the correct manufacturer packages can take time. Outbyte Driver Updater can scan for driver issues and identify available updates; installation through the full version is optional, and driver updates will not replace the correct Kaspersky installation.
If reinstalling Kaspersky fails
A failed installation does not necessarily mean the DLL is the only problem. Check these conditions:
- The installer came from Kaspersky’s official website.
- Windows is fully updated.
- You have administrator rights.
- There is enough free disk space.
- The installer’s digital signature is valid.
- An incompatible security product has been removed or disabled according to its vendor’s guidance.
- A previous Kaspersky installation has been removed cleanly.
- The computer is not blocking the installer through policy or endpoint management.
Restart after removal, then try the correct installer again. On a work computer, ask your administrator for the approved package rather than installing a consumer edition.
If the installer reports an invalid signature, corrupted package, incompatible software, or missing permissions, resolve that message first. Do not bypass security warnings or use an unofficial repackaged installer.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsWhen to use System Restore
System Restore can help when the error began immediately after a known software change and a suitable restore point exists.
- Press Windows + R.
- Type:
rstrui.exe
- Press Enter.
- Review the available restore points.
- Choose one created before the Kaspersky update, failed uninstall, or system change.
- Select Scan for affected programs if available.
- Confirm the restore point and restart Windows.
System Restore is not a substitute for malware cleanup and may not restore a current Kaspersky installation. Reinstall Kaspersky afterward if the product is no longer functional.
Frequently asked questions
Is fssync.dll a Windows file?
No. It is a third-party application DLL historically associated with Kaspersky Anti-Virus. It should not normally be placed in a Windows system directory.
Which Kaspersky product installed it?
Historical records identify Kaspersky Anti-Virus and older Kaspersky enterprise components, including Security Center and Security for Windows Server. They do not prove that every current Kaspersky product includes the file.
Where should fssync.dll be located?
Normally inside the Kaspersky installation directory or a related managed Kaspersky component directory. The correct path depends on the product and installation.
Is fssync.dll safe?
Its name alone does not establish that it is safe. Check the original path, file properties, digital signature, product ownership, and current detection status.
Should I copy it from System32 or SysWOW64?
No. Those are Windows system directories, and choosing between them by guesswork can create a second problem. Restore the file through the matching Kaspersky installer.
Does a 32-bit copy work on 64-bit Windows?
A 32-bit Kaspersky program may require a 32-bit DLL even on 64-bit Windows. Historical records include 32-bit-era copies, but you should not assume the architecture of an unknown file. The matching installer determines the correct file.
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A leftover service, scheduled task, shortcut, or enterprise agent may still reference the old installation. Inspect the startup source and remove the product through its supported procedure.
Can SFC restore fssync.dll?
Normally no. SFC repairs protected Windows components, not an application-owned Kaspersky DLL.
When should I contact Kaspersky?
Contact Kaspersky when the official installer repeatedly fails, quarantine repeatedly detects the file, the product’s signature validation fails, or the exact enterprise package is unclear. Provide the product name, Windows edition, error text, original path, installer logs, and quarantine details without uploading the DLL to an unofficial site.
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