I've heard that someone can use an utility to get the source code from an EXE. To avoid that, do we really need to use a 3rd party products in order to encrypt the EXE? If yes, which one is available.

What I've heard is that someone using an evaluation copy of that product can get the source code from the EXE. In order to avoid that, we need to buy the release of that product so others won't be able to decrypt it. However, I don't remember what was the product name.