The cost of the response to, and recovery from the cyber-attack on the Health Service Executive in May last year has reached almost €43 million and could rise to €100 million.

The figures were released to the Aontú leader Peadar Tóibín on foot of a parliamentary question to the Department of Health.

According to a letter from Fran Thompson, the Interim Chief Information Officer at the HSE, around €12.7 million has been spent on ICT infrastructure, €5.5 million on cyber/strategic partner support, €15.3 million on vendor support for applications and €8.4 million on Office 365.

In his letter to Peadar Tóibín, Mr Thompson said that "the HSE forecasts that the overall cost could be in the region of €100 million and further to this, the implementation of the recommendations of the PWC report into the Conti will require a separate investment case which is being commissioned by the HSE".

Peadar Tóibín described the amount of money involved as an enormous economic cost on the State, adding that it may be only the tip of the iceberg.

"There has been another cost of this crisis, which the government and HSE must also quantify - the cost in relation to health and lives - how many people had hospital appointments cancelled or postponed, how many people died as a result of this cyber-attack?" Mr Tóibín said.

Aontú is calling for a judge-led investigation into the cyber-attack.

"There needs to be accountability here, and we need to ensure that nothing of this nature ever happens again", Mr Tóibín said.

In a statement, the HSE said the cyber-attack had been significant and unprecedented in severity and scale.

"Our next step is to develop a multiyear implementation plan and a multiyear business case around the required investment overall," the statement read.