DISGRUNTLED employees and sympathisers are believed to be responsible for a series of attacks on the Quinn group since Anglo Irish Bank took control of the companies in April.
Gardai and the PSNI have ruled out the possible involvement of dissident republicans in the intimidation campaign, which involves more than a dozen incidents.
Many of the attacks have been described as amateurish and designed to send a signal to the new management of the level of anger felt in some areas at the takeover rather than cause significant damage.
Footage of one incident, in which an arsonist attacked a BMW car owned by Quinn group chief executive Paul O'Brien, showed it took him 20 minutes to set it alight. Another car and the front of a house were also damaged.
The car had been parked outside Mr O'Brien's home in Ratoath, Co Meath, and took place shortly after he and his family went on holiday over the August bank holiday.
Security guards had been posted on the homes of Mr O'Brien and other senior executives after earlier threatening telephone calls but the protection was lifted following a fresh assessment of the dangers to them.
However, they are again under guard since the bank holiday.
The incidents do not appear to be professionally orchestrated and are thought to be the work of locals upset at the fall of tycoon Sean Quinn, who had owned the business empire employing thousands.
One security source asked last night: "Why would the dissidents become involved in a campaign attracting the attention of police both sides of the Border and bring heat down on themselves while they are trying to set up a terrorist campaign against security targets in the North?"
Senior employees also pointed out that Quinn group employees included people from the two communities in the border counties and most were aware that bad publicity about possible subversive involvement in the attacks could frighten off US investors in the companies and earn a poor reputation for the group overseas.
Apart from the Ratoath attack, the incidents have also included setting fire to a number of vehicles at a tarmac plant owned by the group in Ballyconnell, Co Cavan; driving a digger into a weighbridge; damaging a windfarm; burning a transformer; and severed power lines near Kinawley, Co Fermanagh.
Anonymous letters were also sent to some executives working at the group's head office at Derrylin, Co Fermanagh.
After the bank holiday arson attack, the Quinn group issued a statement saying it would not be intimidated by the actions of a small group of thugs and vandals.
Mr Quinn said he had no knowledge of any unlawful acts "in relation to individuals or property associated with the Quinn group, other than what I have read in the media".
He said those responsible were not acting in his name and requested them to stop.