Concerns continue to be expressed about the role of private security firms operating in Iraq.
On Tuesday human rights judge Richard Goldstone called for the work of companies carrying out security work to be better regulated, amid concerns they are out of control and too unaccountable.
Some estimate 15,000 to 20,000 security personnel work in Iraq
Who hires private security firms to carry out work in Iraq?
Anyone from the Coalition Provisional Authority itself to private companies, media organisations and individual UK government departments such as the Foreign Office.
The Foreign Office said it was important to make the distinction between private security firms and private military companies.
The former carry out defensive security work - protecting people and buildings, for example - while the latter is more often associated with the more offensive roles of militias and mercenaries.
How many people are working for these firms in Iraq?
No-one seems to be keeping a tally. The CPA said it does not comment on private security firms.
But there has been plenty of estimation going on. Some reckon there are 15,000-20,000 security personnel in Iraq.
Global Security Risks (GLOBAL) said it has over 1000 skilled personnel throughout Iraq employed in a variety of roles.
Security consultancy Hart Group said estimates ranged up to 40,000, "but it is certainly growing as the number of projects are growing, many of which are being let quickly in the run up to transition of authority".
What kind of work are they doing?
It varies. The Foreign Office, for example, has contracts with two private security companies - Control Risks Group and Armor Group.
Control Risks Group provides close protection security for civilians working with the Coalition, who are employed by or seconded to the Foreign Office.
Armor Group is there to protect UK government buildings in Baghdad.
Many firms are hired by different organisations for similar roles, including convoy protection.
GLOBAL said it was involved, among other roles, in planning and implementation of the Iraqi Currency Exchange Programme, in which the new dinar was distributed while the old notes were collected and destroyed.
Why are private firms used?
Opposition MPs have been quoted claiming the Army is too overstretched to provide adequate protection, hence the need for private companies.
A government source said the situation in Iraq was unusual in that there was an "unprecedented" number of civilians operating there.
And it is not a first - people in Afghanistan also enjoy the protection of private security firms, they said.
Their view is that private firms are qualified to carry out the type of work required, and they do it well.
It makes more sense to hire them as needed, rather than build up the Army to a point that it can carry out civil protection as well, added the source.
In the foreword to a 2002 government Green Paper on regulation of private military companies, UK Foreign Secretary Jack Straw said: "In developed countries, the private sector is becoming increasingly involved in military and security activity.
"States and international organisations are turning to the private sector as a cost-effective way of procuring services which would once have been the exclusive preserve of the military."
Hart's chief operating officer Simon Falkner said private companies were used "because there are not enough military people to do the work".
Why are people calling for private security firms to be better regulated?
Some security workers have complained they are doing an Army-style job but with poorer equipment and training.
Others are concerned that these firms do not all have strict enough vetting procedures when recruiting staff.
Claims have also been made that they sometimes operate outside the law, as they do not have to follow the same 'rules of engagement' as the Army.
However, Mr Falkner from Hart said: "The idea of a bunch of cowboys running around the country shooting people is a myth."
Both GLOBAL and Hart say they abide by the 'rules of engagement,' which outline when force can be used, and both are keen for further regulation.
They must have authority to carry weapons but are not allowed to be heavily armed, and are currently going through a licensing process led by the Coalition Provisional Authority to license all private security companies by 30 June.
What happens if private security companies operate outside the law?
There is no specific UK legislation dealing with this.
A Green Paper in 2002 discussed the regulation of private military companies but found it would be difficult to define the scope of any new measures.
Not enough evidence was found of incidences of bad practice by the companies operating.
Many believe the concerns expressed are already covered by the contracts companies sign, for example with the Coalition authorities in Iraq, or by existing legislation.
GLOBAL said any illegal behaviour was unacceptable and companies should be held accountable, while Hart said that it was difficult to say who should oversee the companies, particularly as there was "no credible police force at present".
Who do the firms employ?
Companies employ a range of people with varying skills.
"All good companies employ only ex-soldiers or policemen," Hart said.
What sort of arms and protection do private security firms use?
Pistols, rifles, body armour and armoured vehicles.