I have always stood on the (X) at the end of a map and get the reward/xp and exit. I recently noticed that people just left after killing the boss, and didn't stand on the (X). I found that I still got xp, and this made xp runs faster.

I keep doing the same run over and over, and noticed that a particular player would keep joining and not move until we were done. He was just sucking the xp off our work. I tried to talk to him, but no answer. He was level 25.

Now, it is possible that he is scripted with something like "autoit" (assuming there is a Chrome Windows DL version, i haven't checked). I have written autoit scripts for my kids to play "neopets" flash games on the web. It's pretty easy to do. I think that what this guy does is create a script that does this:
(1) join a multiplayer game
(2) wait for players to join
(3) wait for all players to leave
(4) quit the game
(5) collect the reward
(6) go back to #1

This is a really simple script. The script would just observer the pixels color changes, and perform the mouse clicks. He can go to sleep at night and wake up to a leveled up character.

Is there any way for STS to prevent this? It's really annoying.