Haw Wu, an analyst at American Technology Research Inc. in Greenwich, Conn., said the synergies between Mercury's products and OpenView "are not as clear" as HP implied. More than 60 percent of Mercury's revenue comes from software development and testing tools, with about 30 percent from application management and just 10 percent from IT governance and resource management, Wu said.

A drop-off in the value of Mercury's stock, which followed the departures of three top executives last year over a stock-option scandal, "produced an opportunity that HP pounced upon," said Zeus Kerravala, an analyst at Yankee Group Research Inc. in Boston.

Nonetheless, Kerravala described the HP and Mercury product sets as a good match. "HP is good at systems and network management but weak in anything application-oriented," he said.