Most anti-virus software bogs down your system and does not allow you to fully use all the power that is available. Grisoft has various versions of this product but I will look over the features of the free version which can be downloaded on their site. (www.grisoft.com) This program performs a daily scan of your computer at a set time everyday at your choice. Depending on the size of the hard drive, it may take 30 mintues to well over and hour. This is the only time when the program will take some resources and slow down your computer a bit. With dual cores now, this is less noticeable. Once it finds files that may be infected, they are either healed or placed in a quarantined area which you may delete the files. It also provides an email scanner to see if anything is a threat from incoming mail. When a file is detected, a message pops up showing the name of the file and degree of threat.
This is a great free program that doesn't slow down your computer. It has kept my computer quite clean and is a great program to look into.