Loyalists have been blamed for leaving an explosive device outside a former prison officer's home in Co Down.
In the latest in a series of attacks by loyalists, damage was caused to the front door of the house at Donaghadee, but nobody was hurt.
The former officer had left the prison service to look after his sister who was left disabled by a hit-and-run car driver in Belfast.
His elderly parents were also in the house at the time the bomb was planted.
Previous attacks on prison staff had been linked to violent protests at Maghaberry jail, near Lisburn, Co Antrim, where loyalists and republicans had demanded to be segregated.
The Northern Ireland Office has agreed to keep the factions apart, but additional security arrangements costing an estimated £7 million have to be put in place and will not be completed until late this year.
Mr Finlay Spratt, chairman of the Prison Officers' Association, said: "The people running around doing these attacks are thugs, cowards and hooligans."