HP says the U.S. Justice Department is investigating the business software unit Autonomy after the computer maker said the business engaged in improper accounting before HP bought it. In a filing with the Securities and Exchange Commission on Thursday, HP said Justice officials had informed the company on Nov. 21 that they were opening an investigation. HP also said that it provided information to the SEC and the U.K. Serious Fraud Office related to "accounting improprieties, disclosure failures and misrepresentations at Autonomy."

HP acquired Autonomy for $10 billion in 2011. The company took an $8.8 billion charge to reflect that the U.K. company isn't worth what it paid. HP says about $5 billion of that charge stemmed from improper accounting.

Autonomy founder Mike Lynch has said he would defend the company's accounts to U.S. Federal investigators.