A bug in IE was exposed to the public back in May by an engineer working for Google.
The exposure lead to the exploitation of the vulnerability by hackers. The bug affected Internet Explorer running on Windows 7 and 8 operating systems, and allowed a hacker to gain the same levels of administrative rights as the current user. This kind of attack would permit an unauthorised party to make setting and rights changes to the victims device.
The engineer who exposed the vulnerability did so as an individual, not as a Google employee, however Microsoft is questioning the responsibility and morality of the engineer in question. Microsoft claim that the vulnerability is best resolved behind closed doors rather than allowing it to get into the wrong hands in the wild.