Flashback, the latest malware affecting more than 600000 devices has been threatening Mac users worldwide. More than half of the affected devices is said to be in the USA.
This malware is said to be a Trojan-horse that exploits loop holes in Java and streams user information, like passwords log-ins, to a third party. This simply happens as the user visits any malicious site. The virus simply gives third party access to your system.
It came disguised as a flash player update and affected more than half the Mac's in the US.
Here's a video explaining it better :
Flashback is not exactly a Trojan horse, it is a downloadable app that opens access to your computer and let the thief grab anything he/she likes.
Those who have accidentally acquired this malware are suggested to turn off their Java to avoid damage.
Apple has also released 'fix's' to cope with this issue, more on that on - SlashGear