Russian antivirus company Dr. Web said the malware, dubbed Trojan.Yontoo.1, is one of an increasing number of such "adware" Trojans showing up, CNET reported Thursday.
Once it has infected a computer, the Trojan generates a dialog box that offers to install a free video player. After users click "continue," the Trojan downloads the Yontoo adware plug-in for Safari, Chrome and Firefox.
The toxic plugin moves additional ads to the user, which creates income for the Trojan's authors if clicked on but also allows outsiders access to track users' Web surfing history.
"Criminals profit from affiliate ad network programs and their interest in users of Apple-compatible computers grows day by day," Dr. Web said in a statement.
Though this Trojan is targeting Mac OS X users, a similar malware targeting Windows systems has been detected, it said.