The head of the country's police watchdog has said he suspects his headquarters were under some form of surveillance.
The former Metropolitan Police officer said it was time to move on from the controversy.
"The terminology of bugged I don't concur with. I certainly suspect, or potentially suspect, that we may have been under some form of surveillance," he said.
Gsoc chiefs were called before the parliamentary body, the Oireachtas Committee on Public Service Oversight and Petitions, to explain suspicions that the watchdog's offices in Dublin city centre were at the centre of a surveillance scare.
Mr O'Brien said the Garda Ombudsman is dealing with an "internal" security risk.
Under cross-examination about the late night security sweep of the watchdog's headquarters, he said knowledge of the operation was restricted to about four or five staff in a "sensible" attempt to keep it confidential.
"At this time we were looking at potentially external risks to information flows being seized or captured, or we being surveilled from externally," he said.
"But it is clearly the case here that we have a problem internally and I suspect that is a real issue."
Justice Minister Alan Shatter last night dismissed as completely baseless innuendo any suggestion that the Garda was behind the alleged bugging of the force's official watchdog.
Mr O'Brien told the parliamentary body that when three issues were identified with telecoms in or around the building it was right to suspect that the Garda may have been behind it.
No Garda involvement was found.
Mr O'Brien later claimed that reports of the controversy may have originated from a source within the watchdog.
"It could be that the person who leaked this (security) report is also responsible for other issues in our organisation," he told the committee.
Three key issues were identified in a security sweep by a UK-based private company last year.
Firstly, a wi-fi device in the Gsoc boardroom was found to be connected to an external network. Although it is not not known how this happened, the device was not used by Gsoc and it could not connect to any of the watchdog's internal systems or databases.
Mr O'Brien said Gsoc installed the wi-fi itself but the issue was related to activity the communications device was undertaking.
The second issue revolved around concerns about the security of a conference call telephone in Mr O'Brien's office.
Mr O'Brien said the security concerns were coming from the outside and tests revealed no other matters of concern and no evidence of any calls being compromised.
No external phone number could be identified linked to concerns on the conference phone.
A third issue related to the vulnerability of UK registered mobile phones in the area of the offices whereby a device could have been used to scan for UK numbers outside the building.
Mr O'Brien was repeatedly pressed on his suspicions about the source of the leak.
"I believe firmly that with the amount of information gone out that it could be highly likely that information has come from documents in Gsoc," he said.
"I don't know if that leak is high level or low level."
Less than seven people had access to the surveillance report, Mr O'Brien said.
Suspicion within the Gsoc headquarters was so rife, Mr O'Brien would only talk about the surveillance threat with the two other commissioners - Carmel Foley and Kieran Fitzgerald - in city centre cafes for fear of being spied upon.
"Because of the threats that were identified to us we completely disavowed ourselves of any use of mobile telephony in looking or talking or having any text data or data about this investigation," he said.
"We disavowed ourselves of ever meeting round a normal meeting table either in my office or elsewhere.
"We ended up having to keep it so tight that we were meeting in cafes on Capel Street to discuss this because the security firms have told us very clearly of threats that can be made on mobile phones with quite low technology."
Gsoc has 85 staff and has two Garda superintendents seconded to its offices to assist investigations.
The committee was told all staff have to sign an official secrets declaration and agree to other standards in ethics rules.