Like I said, I've been using MSE for a while now, and I like it. This is on older systems. But it has been running very slowly on my newest, patched-together PC, so I went back to Avira. This machine has a 3 GHz P4 HT, 4 GB RAM and two 80 GB SATA HDDs, and runs Win 7 Pro x64. MSE took several hours for a full scan, and heated up my processor to levels I did not like. Avira can scan the system in under an hour, and without heating things up. It also seems faster on boot-up.