McAfee is not one of the worst, I use Mcafee and have been for about 5 years and it works FINE!!!!!!!!!!
Damn I wish people would stop bashing programs just because they don't like them. Anyway, no virus program is going to work if you download something and install it that has a virus. However, McAfee is good about stopping these downloads, even if it downloads and has some malicious software in the file, when you attempt to open it McAfee will alert you and ask you if you want to continue running the file(unless it is something new, and I am sure that even the best virus protection will miss something occasionally).
Best case, stay away from Limewire, it has been getting bad about viruses in the past few years. Not only that, why take the chance on getting caught downloading illegal software. You do know that Agency's are now placing files in illegal peer to peer software so that when you download and attempt to execute the file you are caught, no if's and's or butts.