I think he mentioned something about getting the virus from internet explorer?
First of all, if your brother still has some other virus then he should follow Broni's suggestions.
In response to your question, you can get viruses from any of the ways a PC's hard drive is exposed to the outside. That includes surfing on the internet, downloading and installing corrupt programs/files (so IE is involved as the path but is not the cause), emails, using infected CD's, DVD's or flash drives, etc., etc.,.
These days you need to have antivirus and antispyware programs installed, and frequently updated and used. Plus a firewall. And take advantage of the Security measures offered within IE. You could also consider using a HOSTS file and a program like SpyWareBlaster.