A new botnet being built, according to security experts. Trend Micro have warned of a new worm that spreads by exploiting a known vulnerability in Windows.

The DOWNAD.A worm exploits the MS08-067 patch, which was released out of cycle after reports that the flaw was being exploited in the wild. Currently, the vulnerability affects all currently supported versions of Windows and Windows Server.

"Initially thought to be working in conjunction with a Networm variant, WORMˍDOWNAD.A is now believed to be an updated version of an attack from the same criminal botnet gang. More than 500,000 unique hosts have since been discovered to have fallen victim to this threat," said Trend Micro.

Trend Micro claimed that it has found cases of the worm in the US, China, India, the Middle East, Europe and Latin America, and that several home broadband networks have been infected.