In recent months, more and more iPhone owners have found themselves with aggressive notifications on their smartphones. They come from the calendar, but it's not very obvious how they got there, nor how you can get rid of them.
In theory, there are no viruses for the iPhone. Your phone is immune to most infections and vulnerabilities that an Android owner faces, for example. At the same time, it was inevitable that various hackers or malware creators would find a simple and effective solution to strike fear into Apple mobile users. If the "smart" guys make some money off of you, so much the better for them and bad for you.
Predictably, the iPhone "virus" gets into your phone with your consent. I put the word virus in quotes, because it's not really a virus, so much as a significant source of stress. It is reflected in a massive volume of notifications at the most inappropriate times and at the highest volumes. In order to "infect" yourself, when you enter a certain website, you are asked for your consent to have an apparently useful program installed. You agree and don't know where to take off your shirt.
To get rid of the iPhone virus infecting your calendar, the solution is incredibly simple. From the phone's main menu, go to Settings, in the Calendar section and tap on Accounts. Carefully review the Calendar accounts you have installed. In addition to a Gmail, Yahoo, iCloud, or any other email address you have from work, you might also see a calendar with a not-so-special name. "Subscribed Calendars", "Other Calendars", "Click Here...". Tap the calendar you don't know, it's not yours. If necessary, tap once more on the name of the calendar. At the bottom of the screen, choose Delete Account. After a few moments, you solved the case.
Alternatively, depending on the iOS version, you could also delete a calendar directly from the iOS app of the same name. Enter Calendar from your phone's main menu and tap Calendars at the bottom of the screen. You should see an unusual calendar in the On My iPhone section of that menu. Choose the problematic calendar by tapping on the small i - to the right of the name. Select Delete Calendar and confirm the deletion.