Flashback was a Trojan that was easily avoided by practicing safe computing, namely leaving Java disabled in the browser until needed by a trustworthy site. Flashback affected about 1% of Mac users who didn't practice safe computing.
iAntiVirus has a bogus malware definitions list, making their detection accuracy untrustworthy. They also make inaccurate claims about the existence of Mac malware, in order to hype the need for their product.
This post will give details.
All OS X malware in the wild can be successfully avoided by practicing safe computing, without the need for 3rd party antivirus software.