Hewlett-Packard Co. said on Tuesday it had been duped into overpaying for one of its largest acquisitions, contributing to an $8.8 billion write-down and a huge quarterly loss.

The technology giant said that an internal investigation had revealed "serious accounting improprieties" and "outright misrepresentations" in connection with U.K. software maker Autonomy, which H-P acquired for $11.1 billion in October 2011.

"There...