Shareware registration. Sample?

[Deje]

[refractor]

[Conan]

The registry is one obvious place to write your info to but you should make the keys non-obvious & have more than one location. You can also modify a file which does not appear to be part of your secutity with some identifier to indicate registration plus any other method you can think of to disguise the process. In your code you should not embed any literals which can make it easy for anyone disassembling your code to follow how you do the registration checking.