An investigation is under way following an attempt by an unidentified external source to hack into the Garda IT system last week, which forced the shut down of a number of internal systems, RTÉ's This Week has learned.

Gardaí are attempting to determine who carried out the attack, and it remains unclear whether the attack was carried out by an Irish or international hacker or group of hackers.

The attack was conducted using what was described as a new strain of threat previously unseen by the force's IT security team, which prompted the decision to shut down several systems to protect them against any corruption or leak.

The garda computer systems contain highly sensitive data ranging from open criminal investigation files to data relating to members of the public and staff.

However, it is understood no garda data was compromised in the attack but garda management is treating the attack very seriously.

The Computer Crime Unit at the Garda Bureau of Fraud Investigation is investigating the source of the attack, gardaí said in a statement.