Avast! 5 has been noted in many reviews as being a bit heavy on the system. One possible reason is that it scans repeatedly most files that have a “dangerous” file extension, even if “use transient & persistent caching” are both checked. This is not noticeable if the file is small but it can be a nuisance for large files.
It happens when performing the following operations: mouse hover (to get the file properties), delete, copy, move, name change, open, and execute. Maybe other operations too.
I don’t think that such scan is always needed when the file is not actually being opened or executed for then there is no risk of malware action. In any case, if there is a valid reason for such scan it could be made optional or at least the transient caching should work as expected.
Someone said, in another thread that “avast, as an on-access scanner has to get a head start to prevent infection, now waiting only until you attempt to run them might be too late if there happens to be something protecting them when run.”
Come on! A file does not have to be scanned over and over again every time one of the above operations is done, except perhaps when executing and opening. Even when deleting the file?! If something protects the file when run, avast! could issue a warning so that the user stops the operation
This is overkill and most certainly is a factor that makes avast! hog the system. By the way, I only noticed this kind of behavior with version 5.