What are the different free antivirus software available on the internet?

You should have more than just antivirus software, you should also have antispyware and firewall software.

If you need freeware security applications, you can choose from the following:

firewall: (listed in order of preference)

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 blocked. 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: (listed in order of preference)

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

Spybot S%26D (http://www.safer-networking.org ) for additional removal ability.