Be aware that the earlier Versions are lacking in Malware detection/cleaning abilities- these were features added in the 3.0 and 4.0 Versions.
Originally Posted by madshark
2.7? The newer versions add more protection levels, the ability to remove detected viruses/malware automatically, and more in depth scanning as well as malware protection, and self defense to prevent corruption/infection of NOD32 itself- so it may be that you have malware that the earlier modules are not designed or able to detect.
It is really your choice If you want to run an outdated program, but the resource footprint of the newer versions isnt much different than the older versions, and If your paying for the program It seems like a bad idea to run a program lacking in protection when this was the reason for the newer releases. In the end though, it is your system. If your system cannot handle the slightly increased resource footprint then perhaps you shouldnt be running ultimate- try Basic and/or install more RAM.
If this is recent issue, then try a system restore to a point before the problem occured.