Some correctional facilities have been described as hellish “monster factories.” In the face of long-term imprisonment, some inmates can become detached from reality, and a darker side to their personalities may emerge. Violence becomes a way of life – perhaps even more so – and for some incarcerated gang members, prison doesn’t stop them from still carrying out crime.

From drug and weapon trafficking to extortion, intimidation, and murder, these gangs still control criminal empires, despite being behind bars, and prison authorities can feel powerless to stop them. While the following gangs may differ in political beliefs, ethnic makeup and location, one thing they all share is that, in some way, they’re all by-products of the criminal justice system. “I laugh at this system because there ain’t a damn thing that it can do to me except to deal with the monster it has created,” said 26-year-old New York prisoner Willie Bosket in 1988.

Meet the world’s 10 most dangerous prison gangs…

10. Brödraskapet – Sweden

The Brödraskapet gang originated at a Kumla high security prison in 1995. Members of Brödraskapet, or “The Brotherhood,” are known to be responsible for criminal activities including drugs and arms trafficking, extortion, and murder. Despite being a relatively small gang that includes between 60 and 70 active members, The Brotherhood has a strong presence in Swedish prisons and has developed a reputation for violence. The gang is also involved in a wide range of criminal activities beyond prison walls. In 2007, during a party at a Brotherhood clubhouse in Göteborg, an ex-member of another gang was murdered after he allegedly made an insult about a Brotherhood member’s tattoo. While a number of individuals were arrested, just one member and one supporter were found guilty.

9. Mexican Mafia – USA

The Mexican Mafia, also known as La eMe (Spanish for “M”), has been operating in US prisons since 1957, when 13 members from Hispanic street gangs teamed up in a youth correctional institute in the city of Tracy, California. Currently, the Mexican Mafia is believed to be the most powerful gang in Californian prisons, with up to 400 official members and around 990 associates who are involved with its criminal work and aspire to become official members.

In the 1970s, its first killing outside the prison walls occurred. A member of the gang, Alfonso “Pachie” Alvarez, was murdered for keeping drug-dealing “taxes” without distributing profits to others in the Mexican Mafia. Their network also extends to the outside world, as some smuggle drugs behind bars to sell to prisoners. It is regarded as America’s most active gang, as far as number of incidents caused by members goes.

8. Aryan Brotherhood – USA

The Aryan Brotherhood is a white supremacist gang and organized crime group that operates both in and outside of prison across the US. It is thought to have been founded in 1964 by Irish bikers at San Quentin State Prison as a response to the racial desegregation of American prisons. Also known as AB, The Brand or Alice Baker, it is thought that the Aryan Brotherhood has around 20,000 exclusively white male members, some behind bars and some on the outside.

The gang’s prison activities include smuggling contraband, distributing drugs, murder, and prostitution. It also takes part in drug trafficking, pressure rackets, extortion and even dog fighting. Despite comprising only one percent of the US prison population, the gang is believed to be behind about 20 percent of all prison murders. Mafia boss John Gotti allegedly turned to the Aryan Brotherhood for help dealing with an attacker, and the threat was so great that protective custody was arranged for Gotti’s assailant immediately.

7. Nazi Lowriders – USA

The Nazi Lowriders, or NLR, is another white supremacist gang and is found primarily in the prisons of southern California. NLR is estimated to have between 1,000 and 5,000 members and, unlike other racist white gangs, the group has become notorious for being violently proactive rather than reactive. The NLR has grown in strength and influence since government crackdowns on the better-known Aryan Brotherhood. One particularly notorious crime committed by the gang was the beating to death of a black teenager in April 1996 by gang members Danny Williams and Eric Dillard, who followed up the incident by assaulting two black men in July of that year.

During a 2001 raid, 73 guns, hand grenades, body armor and more were found in the home of NLR members Scott Kuhn and Marcello Castellano. While the NLR uses its white supremacist ideology for the recruitment of new members, its main objectives are drug trafficking (especially speed), robbery and extortion. NLR leaders appear to run the gang in a particularly organized and aggressive way, making it a major threat within California prisons.

6. The Ñeta Association – Puerto Rico

Founded in Puerto Rico in the 1970s, The Ñeta Association, or just Ñeta, has gone on to become the major controlling force of the Puerto Rican drug trade. Ideologically, the gang aligns itself with the Puerto Rico independence movement, and members regard themselves as oppressed by the US government. It is estimated that there are 40,000 gang members in Puerto Rico, a further 20,000 in the US, and 30,000 spread out across the rest of the world.

It rose to prominence after a brutal attack against the leader of rival gang G27. Using spoons and their hands to dig, Ñeta members broke into his cell, stabbed him more than 150 times and chopped him up into 84 pieces. Allegedly, parts of the body were sent to various people, including his mother and G27’s second-in-command. Ñeta has a reputation for secrecy, and members are often unwilling to admit their membership. This makes the group particularly difficult to identify, hard to control and even more dangerous.

5. Nuestra Familia – USA

The Nuestra Familia was established in California in 1968, primarily to protect rural Latinos from the Mexican Mafia during their time in prison. These days, the gang’s main activities involve smuggling and distributing drugs into the prisons in which it operates. The Nuestra Familia are fierce adversaries of the Mexican Mafia, and this rivalry is considered the longest-running gang war in California. It’s also estimated that the Nuestra Familia was responsible for at least 600 murders within a 30-year period. Imprisoned Nuestra Familia gangsters have strong links on the outside, and use gang members who have been released to smuggle drugs and contraband into the prison system.

4. Black Guerilla Family – USA

Ex-Black Panther gang member George Jackson founded the Black Guerilla Family with W.L. Nolen in San Quentin State prison in 1966. With a list of stated aims that includes removing racism and toppling the American government, it is acknowledged as the most political of the largest US prison gangs. The BGF’s aggressive anti-authority beliefs make them a serious threat to prison officials, who represent the government that the gang aims to eliminate.

The BGF is known for recruiting members from other black street gangs when they are imprisoned, and has strong relationships with many of these external gangs. According to estimates, there could be as many as 300 full BGF members and up to 50,000 associates. Their activities include drug trafficking, car theft, and murder.

3. Trinitario – US and Dominican Republic

The Trinitario gang was founded in New York prisons in 1989. Originally, the organization was started to offer help and safety to Hispanic prisoners incarcerated in New York. Trinitario translates into “Trinity Brotherhood,” and gang members are Hispanic – predominantly from the Dominican Republic. Trinitario has been described as New York’s fastest-growing gang. It has spread to the surrounding areas (as well as overseas) and is believed to have 30,000 members around the world, with most of these in the US and Dominican Republic.

The gang makes its money through drug and weapons trafficking, witness intimidation, robbery, and murder. Their use of machetes, combined with their strength of numbers and rapidly-increasing membership, makes Trinitario one of the most dangerous gangs out there.

2. Primeiro Comando da Capital – Brazil

Primeiro Comando da Capital (Portuguese for “First Command of the Capital”) is a Brazilian prison gang based primarily in São Paulo. The gang began on August 31, 1993, when eight Taubaté Penitentiary inmates met up at a soccer match. Since then, the PCC has grown to a position where it controls most of São Paulo’s organized crime. The gang’s reach is thought to be spreading throughout Brazil and spilling over into neighboring countries, where its influence is used to facilitate drug-smuggling operations. Within prisons, it is known to be responsible for riots, escapes and murder.

In May 2006, attempts by São Paulo police to find out who was responsible for killing 40 police officers erupted into a bloody battle between members of the PCC and the authorities, with more than 150 people killed over the course of a few days. The violence has been described as the worst of its kind in the history of São Paulo and Brazil. Allegedly, imprisoned gang members used cell phones to mastermind the attacks.

1. The Numbers Gang – South Africa

The Numbers Gang is believed to control most of South Africa’s prisons. Established in 1911, the gang is divided into three factions: the 26s, the 27s and the 28s. Each arm of the gang serves a different purpose. The 26s are responsible for getting cash, the 27s are the law-keepers and the 28s are the warriors. The Numbers Gang is particularly dangerous because of its influence in the prison system and the level of violence the gang demands of their members, being notorious for attacks on prison guards and warders. In Pollsmoor Prison, up to 50 percent of warders have been stabbed or cut. The gang often demands these attacks of new members to prove their loyalty.

The leader of the Pollsmoor Prison 28s is John Mongrel. Mongrel is thought to be responsible for as many as 1,000 killings. The gang is extremely organized, and if members violate the rules, then it will conduct an investigation and “trial”. If the verdict is death, the member is often asphyxiated or has their throat slit. For less serious crimes, the member will have a cut made in their anus in order to let blood, and will then be raped by an inmate who is HIV positive. The transfer of prisoners between South African jails allows the gang’s influence and control to spread.