Chinese government officials have warned ADSL users to install a recent Microsoft security patch after Worm.Mocbot.A - called "Demon Wave" in Chinese - caused massive system failures and disrupted broadband internet access across the city of Shanghai.

The Shanghai Computer Virus Prevention Center issued a special warning last week, urging internet users to download and install the latest Windows security patch from Microsoft's website.

State-owned media reported hundreds of thousands of computers, most without properly updated antivirus software, were hit last week by Worm.Mocbot.A. The worm propagates by exploiting a Windows Server services vulnerability patched by Microsoft last week. It caused computers to crash and disrupted internet access across the city, the reports said.

Once the worm has infected a system, it connects to an IRC (internet relay chat) server and allows an attacker to download files or run applications, Internet Security Services said on its website. The worm, which affects Windows 2000, Windows XP and Windows Server 2003, also consumes a large amount of bandwidth, it said.