Computer local area networks at East Japan Railway Co. and some media organizations were inaccessible Saturday morning, apparently due to a bug in antivirus software made by Trend Micro Inc.

“A bug was detected in a file (designed to detect viruses), and it is highly likely that computer networks that were updated (with the file) encountered a system failure,” the software company said.

Trend Micro said its virus analysis and support center in Manila released the file worldwide at around 7:30 a.m. Saturday as part of an update for its Virus Buster software.

It said the file was replaced by a bug-free one before noon.

The buggy file slowed down computer performance substantially by making CPUs run at almost full capacity, the software company said.

JR East encountered the trouble with its LAN from around 8 a.m. to noon, but train services and ticketing operations were not affected, company officials said.

View Plaza, a travel agency operated by JR East, said it suffered access failure. It asked customers to buy their tickets at JR station ticket offices.

Computer networks at Osaka’s municipal subway system were also affected.

Kyodo News experienced LAN access failure from around 8:20 a.m. to shortly before noon. The Asahi Shimbun and Yomiuri Shimbun also had trouble with their LANs at their Tokyo and Osaka bureaus, but the problems did not affect editing or printing of their evening editions.

The Nihon Keizai Shimbun’s sales bureau and the Shinano Mainichi Shimbun in Nagano Prefecture encountered minor trouble.

The problem also affected absentee voting for mayoral and municipal assembly elections in the city of Toyama, where votes had to be counted manually, while the Tottori Prefectural Government and Beppu City Hall in Oita Prefecture were also hit.

No LAN-related trouble was reported at central government entities such as the prime minister’s office.

Trend Micro said its call center would be open over the weekend. It posted directions on its Web site to remove the bug-infected file from affected computers.

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