I did not know that unix and linux users also use anti-virus.
But here is something called "clamAv"
http://www.clamav.net/lang/en/.


So a unix and linux machine can be affected by virus in near future. Hence we need to be extremely careful, while building downloaed free source code in linux.

Yes, but not for the reasons you provide. Searching LQ should give you access to several AV discussions and threads about how to handle source code verification (trusted repos, signed packages, tarball hashes and GPG signatures).

Here is a list of the main features :

command-line scanner
fast, multi-threaded daemon with support for on-access scanning
milter interface for sendmail
advanced database updater with support for scripted updates and digital signatures
virus scanner C library
on-access scanning (Linux® and FreeBSD®)
virus database updated multiple times per day (see home page for total number of signatures)
built-in support for various archive formats, including Zip, RAR, Tar, Gzip, Bzip2, OLE2, Cabinet, CHM, BinHex, SIS and others
built-in support for almost all mail file formats
built-in support for ELF executables and Portable Executable files compressed with UPX, FSG, Petite, NsPack, wwpack32, MEW, Upack and obfuscated with SUE, Y0da Cryptor and others

=> So I think it checks for suspicious code and executables.
Let ke know if I am wrong.

As far as my understanding goes CLAMAV scans you're email for windowsz virussses .
A windowsz virus can not infected a linux neither UNIX or a MAC computer

Yes ronlau9, my understanding is the same.
In fact, I use clamAV in our file server to remove/quarantine files infected by windows virus.
Our file server is a Linux machine, running SAMBA, which provides file sharing service to windows machines. There is nothing to do with linux/unix virus.

It does bit the key here is the definition of "suspicious code".
It should not be necessary to rehash previous discussions: please search LQ.