Virus and hack protection

 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, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

Remove spam from Calendar on your iPhone

proceed with https://support.apple.com/en-us/HT211076 and forget about software protection for iPhone: until it's not jailbroken, you don't need one

None is needed.

Calendar spam and not a virus.