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.