when i performed a scan yesterday (both quick and full system) the scan logs had numerous files in them that Avast said could not be scanned because they are password protected files. I have not put any password protected files on my computer…so how did they get there. This has never showed up in my scan logs before. I tried to send the files to the chest, I tried to delete them, but it will not let my do anything with these files. I notice some of them are attached to Adobe Flash player. Is this a bug or a virus? I am obviously concerned as it raises the issue of the reliability of Avast…if a program is able to put password protected files on your computer, just how safe is that???
Someone with more experience may add information, but as far as I know ‘password protected’ file are just that…protected.
Some legitimate programs protect their files in that manner. 
Adobe has been password protecting its update for a few months now.