Another malware for mac discovered, second this year. It is called OSX/Keydnap and was discovered by the security company ESET.

It comes as a ziped text or jpg but is really a unix executeable that runs in the terminal and installs a conrolserver, then it waits. As soon as you open another program it asks for admin password. If you provide it gets total control over your mac BUT the builtin in Gatekeeper will protect you if correct configured. In system preferences/security it should look like this (sorry for the swedish). Do not install any thirdparty antivirus/security. A longer article on mac security is here.
Gatekeeper