A patch has just been released for a vulnerability that was discovered in Microsoft's SQL server software. You can download the patch here. This patch addresses a vulnerability that exists in the code that is responsible for parsing backup files. One could use this exploit to execute arbitrary code, like a backdoor, to gain further access to the server or worse.

You can read more about the Microsoft SQL server restore integer underflow vulnerability at Securiteam. You can also get detailed help on patching your SQL server at the Microsoft site.