Where I'm at we're still running a bunch of single-core 2003-era machines with 512Mb RAM. These PCs all have Kaspersky anti-virus software installed, and Kaspersky is killing the performance of the older machines. I know Kaspersky is the problem, because we have a computer lab full of these that also run DeepFreeze, and when I removed Kaspersky from the machines and opted to rely on DeepFreeze alone to protect them it was like I breathed new life into them. Other machines that don't use DeepFreeze are still slow, and an experiment on one of them produced similar results.
Fortunately most of the older machines will be gone in the next year, but I doubt the general situation is likely to improve, as we generally purchase off-lease computers. What we're getting off-lease right now isn't bad ($280 for a Core 2 Duo with 2GB RAM and Windows license), but over time we're always gonna be at end of the performance curve.
So I'm wondering about other's experiences running different anti-virus options on older equipment. When our Kaspersky contract is up for renewal, what can I be looking at as alternatives?