The program is freeware, which means that you can copy it, use it as in many machines as you like, and make as many backup copies as you like! But please, if you're going to copy it, copy the original setup file, so the integrity of the program is maintained.

The disclaimer part is very short... I'm not responsible if the program (PopUp Killer) behaves in some way different from expected and because of that you loose some data, or some of your data gets damaged or... or... or... Yours is responsibility to use the program! not mine, ok?