Lot's of students get caught in this chicken and egg situation.  They need to download a program like Antivirus software but can't do it because the virus has hosed their network connection.  The solution is really simple.  You have to go old school and use Sneakernet.  Get a thumb drive or blank CD-R.  Put on you sneakers and walk down to the lab.  Download the software you need and save it to the thumb drive or burn it to the CD-R.  Walk back to your computer and install the software from the CD or thumb drive.  Problem Solved.