My calendar is notice some viruses alert notifications

Good afternoon hettiararchchilage,

Welcome to the Apple Support Communities!

It sounds like you may have been exposed to a phishing attempt in the Calendar app on your iPad. The "virus guard" app you installed may be part of the problem.

The resources below will help determine which calendar these notifications are appearing in and how to check to see if a profile has been added to your iPhone.

Recognize and avoid phishing messages, phony support calls, and other scams

"If you accepted a suspicious Calendar invitation

If you get an unwanted or suspicious calendar invitation in Mail or Calendar, you can report it as Junk in iCloud.

To delete an invitation that you already accepted, tap the event, then tap Decline or Delete Event.

If you unintentionally subscribed to a calendar you didn't want, open the Calendar app, tap Calendars and look for an unknown or suspicious calendar. Tap the calendar, then scroll down and tap Delete Calendar."

How to delete an app that has a configuration profile on your iPhone, iPad, or iPod touch

If the issue persists, please reply to this thread and we'll do our best to help you!

Take care.

Don’t panic. The problem that you illustrate should be 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.

You might find it worthwhile to protect yourself from similar occurrences by installing one of the better content blockers. Whilst unable to block everything, doing so will considerably reduce the likelihood of this or similar exploits being successful in future.

Browser-based attacks can largely be mitigated by installing a good, trusted, Content and Ad-blocking product. One of the very best and most respected within the Apple App Store - designed for iPad, iPhone and Mac - is 1Blocker for Safari.

https://apps.apple.com/gb/app/1blocker-for-safari/id1365531024

1Blocker is highly configurable - and crucially does not rely upon an external proxy-service of dubious provenance. All processing takes place on your device - and contrary to expectations, Safari will run faster and more efficiently. 

Unwanted content is not simply filtered after download (a technique used by basic/inferior products), but instead undesirable embedded content blocked form download. A further benefit on metered services, such as cellular connections where you data may be capped or chargeable, this not only improves speed but also saves you money.

When using a good quality Content blocker, a high proportion of otherwise inescapable risk when using your Safari browser, or linking to external sources from email, is effectively mitigated/blocked.