Hi,

The method I use is similar except only an up-to-date licence check program needs to be given to the customer. Each customer requires a licence file (holding licence no. etc encryped) when their system is installed. The main program then checks the licence no. and then calls licence check program to see if the licence is currently valid.

My licence check program returns 2 key bits of info:
1) A revision date (of licence check) so this can be checked against the revision date of the main program. This ensures that the end user cannot copy an older valid licence file & use your system (eg. if they were valid user but not now - if they havent paid!)

2) If licence is valid, expired or invalid.

Parameters passed to the licence check are encryped then decryped by the licence check. The licence check encrypts its return value which the main program decrypts. This part is not required if it is unlikely that users will be clever enough to check what the licence check program is returning & bypass it.