I would recommend that you periodically clear your Temporary Internet Files.
The boot-time scan by default scans many files that would otherwise be inert/dormant, Archive files (which this is one) and it also scans for PUPs, which is less likely to be understood by a user.
PUP = Potentially Unwanted Program - See http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci1066761,00.html
. Not included in this definition are tools which can be used for good or evil, some have been legitimately installed for a specifically good purpose, but could have been unknowing installed for a malicious purpose.
Not all antivirus programs scan for PUPs and avast has it turned off by default (an exception being the boot-time scan). So if you get this you have been tweaking the avast settings without knowing what the impact might be.
- With a resident on-access antivirus like avast, the need for frequent on-demand scans and or boot-time scans is much depreciated. For the most part the on-demand scan is going to be scanning files that would be otherwise be dormant or inert. If they were active files then the on-access file system shield would be scanning them before being created, modified, opened or executed.
I have avast set to do a scheduled weekly Quick scan, set at a time and day that I know the computer will be on. If for some reason my system wasn't on, no big deal I will catch up on the next scheduled scan.