Apple computer users may think they have nothing to worry about when it comes to contracting viruses and malware online, but a Russian antivirus company is reporting that 600,000 Macs are currently infected with a nasty trojan horse virus called “Flashback.”
About 600,000 Mac computers have actually been infected and some — about 274 — are actually based in the same city as Apple's headquarters, Cupertino, Calif. About 57% of the infected Macs are said to be in the U.S. and 20% are based in Canada.
There are no visible symptoms for this Mac virus, except for making sporadic connections to unknown servers that can be only seen in the Firewall logs, if any firewall is in place," Boris Sharov, CEO of Doctor Web, told Mashable. "The symptoms also depend on the payload that may be downloaded upon the command from the control server.The bad thing about these types of infections is that it is hard to prevent them without disconnecting one's computer from the Internet all together,"
"Unfortunately, the number of infected computers is still increasing," Sharov said. "This means that users are careless about security patches, and they shouldn't be.Although symptoms are minimal, there are a few things you can do to see if you are infected."
Sources from : http://mashable.com/2012/04/05/mac-flashback-trojan/