The Department of Health spent more than €285,000 guarding its empty former headquarters at Hawkins House after moving to new offices.
The security bill for the building complex continued to run up in the months following July 2018 when staff decamped to their new headquarters at Miesian Plaza on Baggot Street.
The department said that 24-hour security needed to be in place amid concerns the building would be taken over by homeless protesters.
They said there was some technical infrastructure in Hawkins House that had to be maintained until the building could be handed over to the Office of Public Works, who have now taken responsibility for it.
The department's final bill for security at the empty Hawkins House came to €285,996 for an 11-month period.
A spokeswoman said: "In order to support the efficient move to Miesian Plaza, it was necessary to have a period of time when infrastructure and certain contracts were maintained through the transition."
She said the main move had taken place over two weekends in July 2018, but that some technical infrastructure was not "finally decommissioned" until June of the following year.
The spokeswoman added: "In addition, the department was informed by An Garda Siochana that they had intelligence regarding an imminent occupation in the building following a similar situation in Apollo House next door.
"This resulted in a decision to extend the security guard presence to the building to 24/7."
The department said all existing service and energy bills, pest control, cleaning of reception and car park areas had now transferred to the Office of Public Works.
The demolition of the Hawkins House building is due to take place next year.
The department also spent just over €20,000 on pest control services in Hawkins House in the year that they left.
However, the department said most of this had been incurred while staff were in situ, with only a €475 bill from the time the building was empty.
As part of the move, just over €555,000 was spent on laptops and a further €88,129 on phones, according to records.
Ongoing bills relating to their new headquarters have included between €26,834 and €35,857 a month in cleaning costs, and more than €20,000 a month for electricity.
The Comptroller and Auditor General also found that €14.1m in rent and service costs were run up between December 2016 and April 2018 while the building was unoccupied.