The United Nations offices in Geneva and Vienna were infiltrated by hackers last year, according to classified documents obtained by The New Humanitarian.

The breach reportedly began in July 2019, though United Nations employees were not made aware of the strike until the end of August.

The New Humanitarian says 20 machines had to be completely rebuilt and UN staff had to work a number of overtime hours to isolate the data. One employee described the breach to TNH as a “major meltdown.”

One alert received by employees said, “We are working under the assumption that the entire domain is compromised. The attacker doesn’t show signs of activity so far, we assume they established their position and are dormant.”

Dozens of servers, including the human rights wing and human resources department, which contains confidential staff information were reportedly compromised in the breach. The report says that the UN did not publicly disclose the breach, or inform the staff of the hack. Staff were asked to change their passwords.