Advie please

I have recently installed Comodo FP instead of Zone Alarm, following a recomendation from this site.

I had trouble connecting to the Internet and followed several suggestions, eventually connecting.

I have allowed access as required for programmes to work.

I play a few online games, snooker, MOHAA Spearhead, TW 2007 etc.

Last night I was playing TW2007 online and someone posted a message with my username in front of it, indicating that I had sent/said it, when I didn’t.

My question is, did they gain access to my system to do this or is there a way of posting messages, which look as though someone else has ‘said’ it?

Has my security been breached? How Can I check?

I am worried that I may have unsecured ports open.

I am using XP Home SP2, Comodo FP/BO Clean/VE, Spyware Guard, Spysweeper, Spyware Blaster, Super antispyware, AVG 7.5, Spybot S&D,