Windows

Message from webpage!!!?

I constantly keep recieving this mesage;

Warning!!!! Your computer contains various signs of viruses and malware programs presence, you sytem requires imediate anti viruse check! system security will perform a quick and free scanning of your pc for viruses and malicious programs.
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I have looked up previous YAHOO questions etc – i am using my TASK MANAGER to end ask each time it prompts up BUT HOW DO I STOP THIS HAPPENING?

I have a free Mcafee from o2
Windows Security centre all turned ON- firewall,auto update,malware protection and other

Mcafee sucks.
Try getting avast.

fake windows security center