I always save my download files in a separate partition from C. After clicking the install file for v4 the installation aborted because the file wasn't in C:\windows\installer folder. I've probably done close to a thousand installations and never had the program complain because the install file was in the wrong folder. Always a first time I guess. I copied the file to that folder and the install went through from that location. Then after reboot the icon was red and windows said the computer was unprotected. Opening nod32 it said real time protection was off click here to start it which I did. Figured it was a glitch but it kept doing this after every reboot. I got nervous about protection so went back to v3. It wouldn't let me install v3 as it detected a newer version of nod32. I uninstalled v4 with revo uninstaller and v3 installed and ran fine. I realized I had installed v4 over v3, there were no warnings about doing that, and maybe that was the cause of the problems. I uninstalled v3 with revo and v4 installed perfectly with no complaints about the location of the install file. I did a manual scan which was slow because I had advanced heuristics turned on. I read that it can be turned off for manual scans which will then run faster, just leave it on for real time protection. The icon was green after a reboot and the computer runs at a snappy pace. In summary apparently v4 is very sensitive if any trace of previous AV software is around including previous versions of nod32. Revo uninstaller does a good job of removing programs in aggressive mode.