Another thing to NOT do.

I just examined a protection system for folks who write apps in the Borland languages, and want to distribute demo versions. It's the "R & T Software Registration Control". I normally don't tell names of protection systems, but since their website is down, I assume they're out of business, and fair game.

The app that I was examining called 2 methods from their control. The first was to get the days remaining in the trial, and the 2nd was to get the "level" of your license key. (Evidently you can generate keys that are capable of enabling multiple items in an app.) The 1st function returned the number of days left in AX. Well, they populate AX with some huge number prior to the call, so the fix for that was to change the 1st byte of the function to a RETN. Now, when it returns, it checks the number of days left on the trial, and it's some astronomical number, and it doesn't bother to nag you about registering, and most importantly doesn't exit.

The 2nd call returned a value that was immediately and'ed with 3. (Evidently only 3 levels in this app.) Well, as fate would have it, they also passed in a huge value that had the lower 2 bits set, so I changed the 1st byte of that function to a RETN as well. It returned, and'ed off the rest of the bits, saw the 3, and said "Full access!".

Obviously this was more the fault of the main app itself, but it's completely possible that this control required those crazy values to be passed in in AX, and if that's the case, they were completely self defeating. I neutered their entire $99 protection system with a 2 byte change.