If this "virus" is regarding an application then uninstall the application from your profile by disallowing any permissions that it has been granted.
Also, if it is a specific virus / application causing you a problem then you could try a Google search for how to specifcally remove that application.
If all else fails you could contact Facebook to see if they have an answer or close your current profile and start up a new one?
Hope you manage to get it sorted out

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