Phishing alert message

Be extremely careful. That alert is likely a phishing message.

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Hi,

Depending on where the alert originated will depend on how to accurately remove it.

The following resources should resolve your issue:

• Delete spam calendars and events on iPhone
• Recognize and avoid phishing messages, phony support calls, and other scams
• Identify legitimate emails from the App Store or iTunes Store
• Detect and block spam phone calls
• Identify and filter junk mail in iCloud
• How to delete an app that has a configuration profile on your iPhone, iPad, or iPod touch
• About pop-up ads and windows in Safari

Hope this helps.

Exactly where are you seeing the alert?