Scam messages

The problem that you describe likely being very easy to resolve.

It is highly probable that an inadvertent click on a website link has “subscribed” an additional (unwanted) Calendar to your device - and this unexpected Calendar is exposing unwanted calendar events and sending you unexpected “virus” or other warnings. 

Given that infecting a non-jailbroken iPad/iPhone with actual malware is incredibly difficult, this technique is employed by malicious Actors to fool or encourage you into doing something untoward - more often than not, parting with personal or financial information leading to fraud or attempted extortion.

Let’s check for what’s out of place...

iOS/iPadOS13 and earlier: Settings > Passwords and Accounts

iOS/iPadOS14: Settings > Calendar > Accounts

Look for an “account” that shouldn’t be in the list of accounts - as this will likely include the Calendar that contains all the unwanted events. When you find the suspect account, tap - then select Delete Account. This should resolve the problem in its entirety.

I hope you find this helpful in finding the source - and in resolving the issue if an unexpected Calendar is found.