The California-based security software company announced the Justice Department's involvement on Wednesday and added that it plans to delay filing its annual report, known in financial terminology as a "10-K," so it can restate earning for fiscal years 1998, 1999 and 2000 to take into account information from the investigation.

"We don't know when (the Justice Department) became involved," said Jennifer Keavney, a spokeswoman for Network Associates. "We became aware of their investigation this quarter, so we are disclosing that as required. But how long they have been involved, we don't know."

An official from the Department of Justice wasn't immediately aware of the investigation and could not comment. Network Associates stock dropped from $15.38 to $15.02 (£9.75 to £9.52), a fall of 2.3 percent, by late afternoon on Wednesday.

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