Police Federation chairman said he had been 'inundated' with messages from officers after the 'monumental' data breach.
A document detailing the names and ranks of thousands of police officers in Northern Ireland was mistakenly published online on Tuesday.
It has raised concerns for their safety in a place where law enforcement remains the target of sporadic violence.
Police in Northern Ireland said the leaked data included staff members' place of work, surnames and first initials, but not their home address.
The incident occurred while the police were responding to a routine request under the UK's Freedom of Information Act. In its response, it mistakenly published a table containing the details of its employees, potentially visible to the public for three hours.
"We are aware of the concern this will cause many of our colleagues and their families. We will do everything in our power to alleviate these concerns," said Chris Todd, the head of the Northern Ireland police force, on Tuesday evening.
He explained that "the matter is being fully investigated".
The incident comes a few months after the terrorist threat level in the British province was raised following an attempted assassination of a police officer by dissident republicans.
The attack on police officer John Caldwell in February shocked Northern Ireland, where the police remain the target of sporadic violence after being regularly targeted during the three decades of conflict in Northern Ireland.
On Wednesday, the chairman of the Northern Ireland Police Federation, Liam Kelly, described the data leak as "monumental", saying on the BBC that he had been "inundated" with messages from police officers.
"They are shocked, appalled and fundamentally angry that this has happened," he said. "Our officers go to great lengths to protect their identity. Some of them don't even tell their close friends and associates," he added.
They "work under cover of the greatest potential threats, both on and off duty", according to Kelly, "so it's important (...) that the organisation protects them too".