Hello
Thank you for your question and reaching out. I can understand you are having query\issues related to Security Alert.
If there is message on the screen saying to Call number then it may be Scam or your Computer is infected with Virus.
1. Please disconnect computer from Network or Internet.
2. Please start your computer in safe mode and delete all Temp files
-> C:\Windows\Temp
-> %USERPROFILE%\AppData\Local\Temp
3. Within safe mode Got services.msc -> Disable all non-Microsoft services which you think you did not install.
4. Perform Full scan of the computer using Antivirus software and using this Malicious Software Removal tool.
https://www.microsoft.com/en-us/download/details.aspx?id=9905
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