we got an email saying they have blocked port 25, which means we cna't send emial.  i can go around that, find, or use comcast mail online because it doesnt affect that, it is just because we use mail clients...

my brother has a pc, my mother and i have macs... i don't know if that matters.

my brother went to his friends house, and they downloaded aim and i have a suspicion that some other things were downloaded as well, because he's kind of freaking out that it might show webistes if i tried to do a scan... and his history is deleted.  
i'm doing a virus scan now, but really, what is going on with this?  

i'm sorry if this made no sense, but i don't know how to word it as i am horrible with explanations, if someone could help me, i'd really appreciate it, as i'm being punished for not knowing how to fix this.