The warning over cybermercenaries came in an annual report published by Britain's Intelligence and Security Committee, a watchdog body of senior lawmakers that oversees Britain's spy agencies.
Citing testimony from British eavesdropping agency GCHQ, the report described the mercenaries as "skilled cyber professionals undertaking attacks on diverse targets such as financial institutions and energy companies.
"These groups pose a threat in their own right, but it is the combination of their capability and the objectives of their state backers which makes them of particular concern," it said.
The lawmakers didn't name any specific countries or say how widespread the practice was. The report didn't go into much further detail, but there's long been concern over the proliferation of private companies that profit from developing and distributing offensive software.
The report quoted GCHQ as saying that the electronic threat facing Britain is "at its highest level ever and is expected to rise further still" -- a warning that tracks with longstanding trends relating to the growth of cybercrime and increasing official interest in online espionage. As with past reports, lawmakers singled out Russia and China as two countries alleged to have carried out attacks over the Internet.
The report also covered issues surrounding the proliferation of weapons of mass destruction, counterintelligence, and terrorism. It touched on the threat of Islamic radicalism out of Syria, where it said a significant number of British citizens had flocked in order to fight a holy war. It quoted Britain's security services as saying that "individual jihadists in Syria currently represent the most worrying emerging terrorist threat to the UK and the West" and said that there was a risk that the country's stockpile of chemical weapons could fall into the hands of extremists.
Not covered in the report were allegations published by the Guardian newspaper that GCHQ and its U.S. counterpart, the National Security Agency, were engaged in a global surveillance campaign aimed at securing access to as much of the world's communications as technically possible. Some of the revelations raised fears that Britain was swapping data with the United States on its own citizens to get around restrictions on domestic espionage.