why my usual antivrus McAfee rid of Adware?

I usually get rid of an adware trojan viruses easily, but it is a pain in the rear. He will not let me start my computer in normal mode and it appears constantly updated Security yoru orders. Please help.

This will remove the adware Malwarebytes Anti Malware http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?tag=mncol&cdlPid=10896905 FREE EDITION Run a quick scan and delete all infections found

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