Apple today released a fix for a Safari vulnerability on Windows. According to Apple, viewing a maliciously crafted BMP or GIF image may lead to information disclosure. Combined with Internet Explorer, this bug could lead to remote code execution. A pretty nasty situation if exploited.
The update is for Windows only (at this time) however a Macintosh update should come along shortly as well. As it presents a much bigger danger on Windows, it is smart that Apple is focusing on fixing that version first.
Find out the all of the nitty gritty details here.