help I think my java game has been hacked

I was at a game developer's IRC chat room. I needed someone to beta test the game I have been writing for over 3 years. 2 people said they would test it and while they did they were talking about a texture applet that uses XOR.
They didnt provide any worthwhile feedback and said it took 15 mins to download. When I ran the game immediately after this, these huge textured squares appeared on the screen and bounce around and change. When the game launched with webstart the java consol appeared and showed that an applet was downloading from a different address to mine, I followed the link and it was about using the IRC applet I had been on to display private channels. The post was 3 years old but its strange it seems relevant to what happened to my game. Networking and security are not my favourite subjects so I'd really appreciate help with this.
When I ran the game on another pc there was no problem, so maybe just my machine is affected? :cry