Its called desktop tower defense
The key is to stop the creeps from crossing the grid to reach the other side by building things to kill them. Maze patterns are a must. Also, the key is UPGRADING.
When you finish, submit your score under your QJ user name, then, in the groups section, put QJ as the group so we can really compare
Everyone must press medium to play, as easy is too easy, and doesnt record score, and anything else is too hard. So just press medium and play
Here is an example to a maze pattern (you'll get it if you start playing)