HP has agreed to acquire Mercury Interactive for $4.5bn in cash. 

Mercury develops testing and business technology optimisation software that allows IT departments to automate the management of systems. The firm will be integrated into HP's existing software group.

In a conference call discussing the deal, HP chief executive Mark Hurd acknowledged that the two companies have very little overlap, but claimed that HP has been looking to develop software with Mercury's functionalities for some time.

"Mercury has a software business that is almost a perfect complement to our software business. It allows us to take what we believe is a very strong position in the management software business," said Hurd.

Mercury was delisted from the Nasdaq stock exchange earlier this year after it failed to meet filing deadlines for its quarterly results.

The company is in the process of restating its financials as a result of irregularities with its executive stock option programme.

The controversy made the firm a likely takeover target and forced the departure of the company's chief executive, chief financial officer and general counsel last November.

Hurd said that he expects no additional future claims from the option trading scandal.

The acquisition marks the first multi-billion dollar purchase by HP since it acquired Compaq in 2001.

The deal does not mark the onset of an HP buying binge, but makes sense as an opportunity to fill a gap in HP's product portfolio, according to Hurd.

"When you have an opportunity to acquire a property such as Mercury, you take advantage of it," he said.