Dealing With Funny Checksum

After a while, I've decided to write about something interesting which I've found while unpacking one protection, and it will be also nice introduction to one of my tools which I have wrote for fun of it.

However, I won't mention application name here, but to demonstrate checksum check which I have found I will be using one test application, thus you will get idea what happened, and how checksum is defeated. I will also introduce one tool I wrote, which served me well in this particular case. Tool should come with this document, thus I won't describe tool, and it's internals as source code should be well commented.