An internet-borne infection has devastated thousands of computers across the world.
Security officials say the virus-like worm, dubbed LovSan, is part of a co-ordinated attack exploiting one of the most serious flaws discovered in Microsoft's Windows operating systems.
The worm was first reported in the US yesterday and, while appearing not to delete files or otherwise incur permanent damage, knocked many computers offline.
Across Asia and Europe, it has struck many businesses as they opened and workers logged on, spreading without the need for user intervention.
Computers infected by LovSan are programmed to automatically launch an attack Saturday on windowsupdate.com, a website Microsoft uses to alert customers of software patches that can prevent such infections.
The virus was dubbed LovSan because of a love note left behind on vulnerable computers: "I just want to say LOVE YOU SAN!"
Researchers also discovered another message hidden inside the infection that appeared to taunt Microsoft Chairman Bill Gates: "Billy Gates why do you make this possible? Stop making money and fix your software!"
Microsoft had posted a free patch on the Web site to protect Windows users after it warned on July 16th about the flaw. Nearly all versions of Windows are affected.