Chosen Answer:
Very bad!! 2 anti-virus programs on one computer will conflict with each other & leave open holes in system security that a virus can & will exploit…
Pick 1 anti-virus program and remove the other. Much better, much safer. And your computer will run more efficiently as well! 
by: Mr Unknowable
on: 13th May 11
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No. Running 2 resident antivirus programs at the same time can cause conflicts.
Very bad!! 2 anti-virus programs on one computer will conflict with each other & leave open holes in system security that a virus can & will exploit…
Pick 1 anti-virus program and remove the other. Much better, much safer. And your computer will run more efficiently as well!
Technically it is a bad idea. The problem arises when one anti virus picks up a virus and stores it on its vault, the other one will see it and try to remove it. Also I have heard that virus definitions conflict with each other. However, best buy used to sell both spy sweeper for spyware and trend micro for anti viruses. They seemed to work well but now days just about every anti virus detects most types of infections. In the end, I have seen viruses get through every anti virus, even macs. Something is something, in the end, it is only your judgment that will prevent a virus from getting in your computer in the first place.