Army personnel fear losing their jobs after they had their details hacked in a cyber attack on the Ministry of Defence (MoD).
Personal data of service personnel and veterans, including names, bank details and addresses, was in the payroll system which was accessed in the large-scale hack.
Barings Law said it had signed up more than 1,000 claimants who were potentially affected. Up to 272,000 service personnel may have been affected by the breach.
Adnan Malik, head of data breach at the Manchester-based law firm, said: “There is a lot of anxiety and confusion for people who may have been affected in what could be a major breach.
“We are receiving hundreds of inquiries every day. Some are serving members of the armed forces who feel let down, others who have high security clearance are afraid they could lose their jobs.
“Their livelihoods are at risk, and they do not know how much of their personal information could have been shared online.
“It can be easy to forget when we see these huge Government data breaches that real people are impacted. We know how scary this is for them and want to help as many of the personnel who are affected as we can.”
Defence Secretary Grant Shapps apologised when the cyber attack was revealed on May 7 and said a full investigation had been launched.
Mr Shapps said “state involvement” could not be ruled out, amid speculation China carried out the hack, and said there was evidence of “potential failings” of the contractor operating the payroll system, “which may have made it easier for the malign actor” to gain access.
Earlier this month, a spokesman for the Chinese embassy said claims Beijing was behind the attack were “completely fabricated and malicious slanders”.
Initial investigations found no evidence that data had been removed, but affected armed forces personnel were alerted as a precaution.
An MoD spokeswoman said: “We are unable to comment further whilst an investigation is ongoing.
“Our people are our priority and we are providing personnel with specialist advice, guidance and support along with access to a commercial personal data monitoring service for those potentially affected.”