n the aftermath of last month's attack on the U.S. diplomatic mission in Benghazi, which killed the U.S. ambassador to Libya and three other Americans, critics have seized on the hiring of a little-known British private security firm now accused of providing inadequate protection at the mission.

The clear industry aim is to distance itself from groups such as that led by former British soldier Simon Mann, who was captured in 2004 by authorities in Zimbabwe as they apparently headed to Equatorial Guinea to mount a coup.

The word "mercenary," Brooks makes clear, is simply taboo.

"Calling private security contractors mercenaries is clearly derogatory and serious journalists and academics don't use the term," he says.

The most vulnerable firms, many in industry say, may be those who have relied on ongoing U.S. military work that is now drying up as the Pentagon "Operational Contingency Allowance" - the additional funding earmarked for the wars - tapers off.

At its peak, the U.S. Commission on Wartime Contracting, a bipartisan legislative commission established to study wartime contracting in Iraq and Afghanistan, estimated there might have been as many as 260,000 contractors in the two countries.