The technical term is "mercenaries."

From yourdictionary.com:

1. One who serves or works merely for monetary gain; a hireling.


2. A professional soldier hired for service in a foreign army.

From the LA Times:

WASHINGTON — The U.S. government's use of private military contractors to conduct interrogations in Iraq and to transport suspected terrorists creates "rule-free zones" and allows abuses to go unpunished, Amnesty International charged Tuesday.

There are 20 known cases of civilian contractors suspected of committing criminal acts while handling detainees in Iraq and Afghanistan, but only one has been prosecuted thus far, said Larry Cox, Amnesty's U.S. executive director.

"Amnesty International is not opposed to the use of private contractors," Cox said at a news conference to release the group's annual report on human rights. "But the reliance of the United States government on private military contractors has helped create virtually rule-free zones sanctioned with the American flag and firepower."

The human rights organization said its research also showed that at least 25 American companies appeared to have been hired by the U.S. government to transport suspected terrorists to countries known for human rights violations, a practice that might make them "complicit in the U.S. government's practice of outsourcing torture."

The CIA has come under intense international criticism for the practice of "extraordinary rendition," in which it captures terrorism suspects in one country and moves them to another for interrogation and detention. Less attention has been paid, however, to private companies whose airplanes and other transportation services have been used in the CIA's program.

Private military contractors based in the United States and other countries have been a controversial presence in Iraq. Their role has come under greater scrutiny after four employees of Blackwater USA, a North Carolina-based security firm, were killed and two of their corpses hung from a bridge in Fallouja in March 2004.

An estimated 25,000 private security workers are employed in Iraq, costing nearly $50 billion since the start of the war. Estimates based on government reports indicate that more than 200 have been killed.

Now guess what; there's an international treaty against mercenaries: The International Convention against the Recruitment, Use, Financing and Training of Mercenaries, signed 4 December 1989. The US does not appear to be a signatory of that.

On the other hand, we did sign the Geneva Convention, and it would do well for Americans to be familiar with that.

We're responsible for the conduct for our prisoners of war, despite our use of mercenaries.