Facebook chat?

[Tim]

There is no need to panic about it being a virus because it most likely isn't. Sometimes when you log-out of websites (in this case Facebook) there can be a delay with the server keeping the users status as online. This is one possible scenario.

The second scenario would be that the account is still logged in on a device or application. Perhaps applications such as Spotify may cause this issue. To resolve this you can simply change your password on Facebook, you will then be presented with the option to log-out of all device/applications. Changing your password on a monthly basis will keep your account secure.

Good luck!