What is the best open source antivirus software? best open source internet security software package?

If you need an anti-virus, download AVG 8 Anti-virus:
http://www.free.grisoft.com

And for spyware, get SpyBot – Search and Destroy:
http://www.safer-networking.org/en/mirrors/index.html

Both are free, as powerful as paid programs, such as Norton and McAfee, and don’t use up as many resources.

Good Luck.

Kaspersky antivirus is one of the best antivirus out there
Refer this
http://anti-virus-software-review.toptenreviews.com/

And i definitely feel there is no need of internet security suite
Kaspersky provides protection from anti-virus and anti-spywares and for intrusion and firewall purpose use
Comodo personal firewall,its free and really superb
Download it from here
http://www.personalfirewall.comodo.com/

Good Luck

If you want opensource try Clamwin, http://www.clamwin.com/.
As long as you are running a decent antivirus and a firewall, internet security software is useless. Just alot of schlock for people that don’t realize they can protect themselves with free programming that is alot less intrusive.