My calendar is showing I have lots of virus. Should I do something about this?

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14 or higher, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

The Apple support article is below. 

Remove calendar spam

Video support

stedman1 gave you the right tools you need to removed calendar spam. What you should do in the future however is NOT click on links from websites you don't confidence or familiarity with. It was you who downloaded the Calendar Spam to your phone doing so. Be careful clicking on things.