The update caused some computers to seize up due to a bad pattern file, according to Michael Sweeny, a spokesman for the the company, which is based in Japan. The faulty update affected computers running Windows XP Service Pack 2, along with Trend Micro's PC-Cillin or OfficeScan software.
Sweeny would not give an estimate to how many computers were affected, but did say that the problem was worldwide.
''It's an antidote to malware threats -- viruses and worms and bots,'' says Sweeny. ''These bots are new and we're trying to protect customers from being vulnerable to personal information threats and zombie PCs.
The faulty update was live on the Trend Micro Web site and was being sent out to customers through its automatic update service for an hour and a half before it was pulled down, according to Sweeny.
The problem was more widespread in Asia since the update wasn't distributed until 3:30 pm. PST on a Friday -- too late for most offices in the West to install it.
A working version of the update was later posted on the site. Customers still having trouble can go to the Trend Micro site and follow the links, or they can go straight to this site.