I've had these problems with McAfee in the past too. Uses too many resources and has a tendency to break network/internet connections if you use the firewall feature. Symantec does seem better but it's a resource hog too. I've had decent luck with the MS Security Essentials, Avast, and AVG.

>The last place I worked used McAfee. Every Thursday afternoon they would run a mandatory scan. It took all the resources on the PC and made it impossible to do any work.
>
>>Just got through troubleshooting a client's laptop, a nice Dell with McAfee SecurityCenter factory-installed. Was running fine until yesterday, suddenly she couldn't get on the Internet.
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>>Turned off McAfee Firewall. Ran multiple diagnostics, troubleshooters and configuration tests. Problem persists.
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>>Completely uninstalled McAfee - problem instantly fixed. Now running MS Security Essentials.
>>
>>If you're using McAfee consumer AV, do yourself a favour and get rid of it before it bites you.
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>>This is not the first time I've personally seen McAfee impair the functionality of a customer's equipment. My understanding is Symantec is a little better since the major '09 rewrite but I still wouldn't touch it with a barge pole, either.
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>>Antivirus is evil, plain and simple. Use it as little as you think you can get away with.
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>>What's particularly scary is Intel bought McAfee, and is making noises about baking McAfee AV technology right into motherboards.
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>>/SET RANT OFF