Your regular Windows Update already includes the Windows Security (or Windows Defender Security Center in previous versions of Windows 10) signature files, but if you want to update only the security signature files:
- Select Start > Settings > Update & Security > Windows Security > Virus & threat protection.
- Select Check for updates (or Virus & threat protection updates in previous versions of Windows 10).
- Under Security Intelligence, select Check for updates.
- If Windows Security finds a new signature, it will download and install it.
- The update completes with the new signature. Keep these points in mind.
Note: If you get an error message while trying to download or update a signature, wait for at least one hour and try again or update signatures manually.
Also, make sure the signature you want to download is 50 MB or larger to ensure you get the complete signature file.