(Reuters) - Frustrated by their inability to stop sophisticated hacking attacks or use the law to punish their assailants, an increasing number of U.S. companies are taking retaliatory action.

Known in the cyber security industry as "active defense" or "strike-back" technology, the reprisals range from modest steps to distract and delay a hacker to more controversial measures. Security experts say they even know of some cases where companies have taken action that could violate laws in the United States or other countries, such as hiring contractors to hack the assailant's own systems.

In the past, companies that have been attacked have mostly focused on repairing the damage to their computer networks and shoring them up to prevent future breaches.

But as prevention is increasingly difficult in an era when malicious software is widely available on the Internet for anyone wanting to cause mischief, security experts say companies are growing more aggressive in going after cyber criminals.

"Not only do we put out the fire, but we also look for the arsonist," said Shawn Henry, the former head of cybercrime investigations at the FBI who in April joined new cyber security company CrowdStrike, which aims to provide clients with a menu of active responses.