Williams, from Finglas -- who is serving a lengthy jail sentence after he admitted preventing gardai chasing a teenage boy who he had handed a firearm to -- says on his Facebook profile that he is "banged up for five years."
Most of his online friends are women but sources say that there are also "deep concerns" that Williams has been using Facebook to issue threats to people.
It is understood the prison authorities have now launched a probe into the gangster's online activities and he now faces tough disciplinary action.
Father-of-two Williams has been in custody since last July when he was handed a six-year sentence for his latest crime -- just one of 106 previous convictions.
The hood is linked to some of the northside's biggest gangs, including that led by jailed Finglas brothers Wayne and Alan 'Fatpuss' Bradley.
He has been shot at, stabbed in the face and beaten up -- but he also has convictions for shooting at a garda, armed robbery and firearms offences.
Last July, Dublin Circuit Court heard that gardai were on patrol in Finglas on December 11, 2009, when they noticed Williams in an area known locally as Charles Lane.
They saw him hand a gun, which was partially concealed in a white sock, to a teenage boy.
Williams saw them coming and the second man escaped while Williams prevented gardai chasing the teenager by throwing a bicycle at them.
Gardai later recovered the revolver, along with six cartridges, from the driveway of a nearby house where it had been thrown.
Sources say the boy who collected the firearm was wearing his school uniform when the handover took place and that if gardai had not taken the gun off the streets, it may have been used in a gangland hit.
A prolific car thief in his younger days, Williams from Barry Avenue, Finglas, was targeted by a vigilante gang in 2001, when he was only 18.
Six men wearing ski masks and balaclavas bundled Williams into the back of a Hi-Ace van, stolen six weeks before.
He was savagely attacked, beaten on the head and body with a hammer, beaten with wooden clubs and slashed from chin to ear with a knife.
Sources say that Williams, who is a chaotic drug user, formed loose alliances with many gangs in the Finglas area.
For a while he was particularly close to murdered local brothers Graham and Alan McNally, who were shot dead in January, 2009 and February of last year, respectively.
Dad-of-two Williams is suspected of being behind a spate of petrol bomb attacks, shootings and assaults over the last couple of years.
In one incident, detectives seized a loaded AK-47 assault rifle and ammunition that he had hidden under the bed of an unsuspecting female relative.
Gardai couldn't get enough evidence to charge him.
No stranger to prison, Williams was jailed for five years in 2006 for his role in an attempted robbery of a petrol station during which a garda was shot in the hand.
It emerged that Williams hid in the roof of a toilet for three hours and waited for the Statoil shop to close before emerging and threatening the night attendant with a gun.
Gardai were called by late- night customers who saw a number of raiders inside the shop. As the men attempted to escape, Garda Joe Glackin received a gunshot wound to the hand which required more than 20 stitches.