If I'm not mistaken, an illegal license key will be blocked when the program updates (e.g. 4.6.665 > 4.6.691) released but as you know it takes for a quite long time, so during that time an illegal license key can be used to updating VPS via auto iAVS update as a legal key.
So it would be a lot better if an illegal license key will be blocked as soon as possible by doing something such as updating a small part of program to avast! for checking license key from time to time (e.g. every week).
When the small, fast, true incremental update is one of the best thing of avast! so if people illegally use avast! Pro but can't perform the auto incremental update via the internet so they may change their mind and do the right thing instead.
The true but sad story is that, I've introduced avast! Home to the people I know but I've found that most of them always change to avast! Pro and try to use illegal license key.
As I said before, those people don't really take advantage from avast! Pro, they don't even know how to use enhanced interface, don't know how to use PUSH update, they simply think that Pro can detect viruses better than home edition.
It's sad to see....