A known flaw in Internet Explorer could be exploited by software published on the web late yesterday.

The code, posted yesterday to the Milw0rm.com website, exploits a recently patched flaw in Microsoft's browser. It could be used to run unauthorised software on a PC that wasn't updated with the latest Microsoft patches, security experts warn.

The vulnerability was first discovered by security researcher HD Moore who posted code last July that could be used to crash the browser. Microsoft patched the flaw in February, but some researchers say it will get more attention from criminals because of this latest exploit code.

"This type of vulnerability has been very popular with malicious attacks in the past and we expect to see its usage increase substantially, now that exploit code is publicly available," security vendor Websense warned.

Researchers at eEye Digital Security Inc. say the Milw0rm code works on IE6, but not on the latest version of Microsoft's browser.

"We've tested it against IE 7.0 and haven't got it to work yet," said eEye's Andre Protas.

Protas said that more reliable exploit code likely will be published in the future.