Experts at security company Trend Micro have warned of a new worm that spreads by exploiting a known vulnerability in Windows.
The vulnerability affects all currently supported versions of Windows and Windows Server.
"A few days ago, Trend Micro got wind of a .DLL worm detected as WORM_DOWNAD.A that exploits the MS08-067 vulnerability. Its routines have led our security analysts to postulate that it is a key component in the development of a new botnet," said the company.
"Initially thought to be working in conjunction with a Networm variant, WORM_DOWNAD.A is now believed to be an updated version of an attack from the same criminal botnet gang."
Fresh reports suggest that the threat has extended its reach around the globe. "More than 500,000 unique hosts have since been discovered to have fallen victim to this threat," said Trend Micro.
The worm spreads within other malware packages but, once activated, it takes over office networks by exploiting the Microsoft flaw on unpatched systems, allowing it to build up large numbers of infections quickly.
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.
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