Microsoft is suddenly serious about tackling RT Jailbreak, a slick tool that unlocks Surface tablets using a hack publicised just days earlier.

A spokesperson for Microsoft’s Trustworthy Computing Group, tasked with Windows security, told The Register that Redmond is “actively investigating” the RT Jailbreak Tool v1 cooked up last week. Microsoft will take “appropriate action as necessary”, the spokesperson said, but provided no further details.

RT Jailbreak is batch file created by a coder called Netham45 that can crack locked-down Windows RT tablets in a matter of seconds. Once in, users can run any unauthorised desktop apps on their ARM-powered devices. Microsoft would rather people download and install authorised, and cryptographically signed, software specifically built for touch-driven computers from its official Windows Store outlet.

The jailbreak tool disables the signature check in the kernel to allow any software to run. It uses a debugging trick published last week by a security researcher known as C. L. Rokr, although the original hack entailed getting one's hands dirty with WinDbg. Netham45 tidied up the process and packaged it as RT Jailbreak Tool v1, which was released just four days after Rokr went public with his or her discovery.

Microsoft appeared to brush off the Rokr hack at the time, saying it wasn’t a security vulnerability - even though it exploited an existing shortcoming in the Windows kernel. “We applaud the ingenuity of the folks who worked this out and the hard work they did to document it. We’ll not guarantee these approaches will be there in future releases,” Microsoft noted.

Redmond's now heightened concern over the new tool may be because it is not quite so inaccessible to "the average user" as the original exploit, allowing punters to install all sorts of ARM-compatible software without the need to trouble the Windows Store. ®