Is there any free anti-virus software?

Some of these programs, such as Avast and AVG, have free versions with basic protection that are available for noncommercial use.

The free versions do not offer technical support and may not offer protection from e-mail spam and hackers, and from identity and information theft. They are usually enough for casual surfing and online social networks. You can also download full trial versions of some programs, after which you can either buy them or continue with the limited free version.