The sitecore\virtualssuser is a user created for making Screen Shots, When you use Content testing, you see a screenshot of the page.
When I do this I don't see the virtualssuser in the /sitecore/client/Applications/LicenseOptions/KickUser.aspx
But do you see the user there? perhaps you have a issue with some pages that keep loading and never or very late ends? or there is a issue with a Specific Sitecore version??.
Where do you see the virtualssuser ?
What Sitecore version are you using,?
Do you use Content testing?
Unfortunately I am going to refer you to