Ofcom confirmed on Monday that it had been hit by a cyberattack by Russian hackers which affected the likes of British Airways, the BBC and Boots in early June.
Data from some 412 Ofcom employees was downloaded during the attack by the Clop ransomware group, according to the broadcasting regulator.
"A limited amount of information about certain companies we regulate” was also taken, Ofcom said, “some” of which was confidential.
International Consolidated Airlines Group SA (LSE:IAG) owned British Airways, Walgreens Boots Alliance Inc (NASDAQ:WBA) and BBC staff were among over 100,000 people affected by the attacks on June 5.
Hackers had broken into MOVEit, a business software programme used to store and move sensitive documents, including bank details and national insurance numbers.
"We took immediate action to prevent further use of the MOVEit service and to implement the recommended security measures,” Ofcom added on Monday.
“We also swiftly alerted all affected Ofcom-regulated companies, and we continue to offer support and assistance to our colleagues.”
None of Ofcom’s own systems were compromised, with no payroll data anticipated to have been stolen.