To gauge its extent can be a very inexact endeavour.
The story of Steve Collins and his family revealed a chilling insight into intimidation at its most sinister.
For taking on a major criminal figure, for giving evidence in a court case which led to his imprisonment, the Collins family were subjected to a reign of murder, arson and constant harassment.
Even with round-the-clock armed protection, life became unbearable, and the Collins’ are now starting a new life on the other side of the Atlantic.
But there are many others who still live unknown lives of fear in Limerick and who keep quiet.
The McCarthy-Dundon gang have used terror against their enemies and also against those they have inveigled into their ranks.
One such person was James Dillon. He came from a fine family background, did well at school and was doing well at an apprenticeship.
When he came to the attention of the gang, they saw him as ideal foot-soldier fodder, with no record to attract the attention of the gardaí.
They befriended him and gave him the use of nice cars.
Bit by bit, the gangland web began to take a firm grip on his life.
Through a mix of flattery and intimidation he was walked into the darkest of crime.
On the morning of Apr 9, 2009, he was told he was to go on a very important mission with a senior gang member.
Dillon was driven to the Roxboro shopping centre and given a powerful Glock semi-automatic.
He was then told to go into the Coin Castle amusement arcade and shoot Roy Collins, 35, who had been pointed out to him beforehand.
Dillon was jailed for life in 2010 for the murder of Roy Collins.
The gang boss who set up the murder was arrested, but released as Dillon refused to identify the others involved in the crime, due to intimidation.
Many families have moved out of gang black-spots such as Southill, Ballinacurra Weston and St Mary’s Park, fearing their sons and daughters could also come under the sway of sinister criminals.
While the gangs, in particular the McCarthy-Dundons, have committed murder and wreaked fear in Limerick since 2000, time and the law has gradually caught up with them.
Most of the McCarthy-Dundon gang are now either in jail or dead.
There are now only two known senior gang figures at large — one in Moyross and the other in Ballinacurra Weston.
The gang figure in Weston was responsible for ordering the murder of nightclub security man Brian Fitzgerald.
Mr Fitzgerald lost his life because he refused to give in to intimidation.
He was gunned down outside his home at Brookhaven Walk, Corbally, on Nov 29, 2002.
The gang leader wanted Mr Fitzgerald dead as he had given a statement to gardaí about a threat made by the gangster against him.
Mr Fitzgerald took a stance against drugs being sold in the city centre nightclub where he was head of security.
His refusal to withdraw the statement cost him his life.
The man who ordered his murder fled to England, where he spent a lengthy spell in jail after being caught trading a powerful gun.
He has since returned to Limerick and has been keeping a very low profile.
The McCarthy-Dundons know no low. They even targeted people who got money from the Redress Board over their treatment in orphanages.
At least one case is known to gardaí in which the unfortunate victim was forced, through terror and intimidation, to hand over all his compensation money.
No case could be taken as the victim was in fear of his life and kept his silence.
But the fortunes of the McCarthy-Dundons began to unravel within the walls of Limerick prison when former associate Jimmy Collins and his sons had a major falling-out with some of the Dundons which resulted in at least one very violent clash.
The McCarthy-Dundons are now finding out to their cost the truth of an age-old truism. There is no honour among thieves.