What is the best free antivirus security software that can be down loaded from the net?

can two different antivirus software work at the same time?

What is the best free antivirus security software that can be down loaded from the net?antivirus

here are some recommendations from available freeware:

firewall:

Comodo (http://www.comodo.com), or

PC Tools (http://www.pctools.com/firewall)

Comodo recently released version 3.0 of its firewall, which adds an intrusion prevention component that's very effective, though it does take time for it to learn your system, and requires some ongoing attention by the user to make sure programs don't get improperly block. Comodo is one of the strongest firewalls available, freeware or commercial, according to the independent testing site matousec.com.

antivirus: (listed in order of preference)

Avira (http://www.free-av.com)

AVAST! Home (http://www.avast.com)

AVG (http://free.grisoft.com)

all provide realtime protection and automatic updates; all have ICSA and VB100 certification, but Avira has been among the highest rated in tests by several respected US and UK computer publications.

antispyware:

Spyware Terminator (http://www.SpywareTerminator.com) or

Spyware Doctor (http://pack.google.com)

either one will give you good, realtime protection, along with

Ad-Aware Free (http://www.lavasoftusa.com) and