MEP Luke Ming Flanagan says he has given Belgian police details of what he calls "an unauthorised login" to his Twitter account.
The investigation by police in Brussels comes after a late-night tweet about former Green Party election candidate Saoirse McHugh appeared on Mr Flanagan's Twitter account.
His account tweeted “Sapirse mchugh photo skinny dipping" (sic) at 2.50am on Monday, but the former TD claimed he had been hacked.
Today, Mr Flanagan said in a statement that his account had been accessed from Belgium, while he is in Ireland. He said that the European Directorate-General for Security and Safety was assisting him with the police investigation.
"A parliamentary assistant of mine along with an appointed investigator from DG SAFE met with the Belgian Police on Wednesday morning.
"I have now established that my Twitter account had been logged into on a third-party app called Tweetcaster. This app allowed an individual to tweet from my account using an old password.
Belgian Police Investigation into the unauthorised use of MEP Luke ‘Ming’ Flanagan’s Twitter account. pic.twitter.com/AaKQrUrXMy— Luke 'Ming' Flanagan (@lukeming) October 2, 2020
"This app was used twice to access my Twitter account from Belgium on September 28, the same day that an unauthorised tweet was posted and then deleted from my account.
"At the time the tweet was posted and then deleted, I was in Ireland and have been since March of this year due to Covid-19 restrictions.
"The police have been provided with the Belgian IP address associated with the use of my account on the Tweetcaster app on that day. They are now working with me to establish the exact location and identity of the individual who has carried out this malicious act of vandalism on my good name."
Ms McHugh has since said Mr Flanagan made contact with her to explain what had happened and she accepts his explanation.