Anti-Virus software??

I was just wondering what anti-virus & firewall software people were using cos I'm currently using McAfee, which is great for comprehensive protection, but has flaws with its virus scan - it will just randomly start and use 75% of my computer's power to scan for viruses as fast as humanly possible. This causes random, huge fps lags for no apparent reason. So, what do other people use that doesn't have this really really annoying feature??
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