Travel trade organisation Abta has confirmed that a cyber attack on its website could have hit more than 43,000 people.
Around 1,000 of these are files may include personal identity information of individuals who may have made a complaint about an Abta member.
Abta said the vast majority of the 43,000 relate to people who have registered on Abta.com, with email addresses and encrypted passwords, or have filled in an online form with basic contact details.
The cyber attack happened on February 27 and Abta has set up a helpline for people concerned over hacked information.
Abta chief executive Mark Tanzer said in a statement: "We are not aware of any information being shared beyond the infiltrator.
"We are actively monitoring the situation, but as a precautionary measure we are taking steps to warn both customers of Abta members and Abta members who have the potential to be affected."
What do I need to do?
Abta has advised members who registered at Abta.com that they should change their password immediately.
It warned that if you are an Abta member who used its online self-service facility to upload supporting documentation relating to membership, data may have been accessed. Abta recommends “remaining vigilant” regarding online and identity fraud: actively monitor your bank, social media and email accounts.
“We are providing any individuals within Abta members who may have been affected with free access to a credit monitoring and identity theft prosecution service,” it said in a statement. “We have contacted, by email, every Abta member who we believe has the potential to have been affected with specific guidance information.”
Pete Turner, consumer security expert at Internet security firm Avast, said: “It’s bad enough if you have to complain about your holiday to ABTA but then to potentially have your personal information compromised will be of concern to many people.
“While it is good that ABTA has already taken steps to not only notify the Information Commissioner and police, but also set up a helpline for people to call if they are concerned, the fact is that consumers can no longer trust companies to keep their data safe. The regular news stories hitting the headlines of data breaches is example of this. It’s important for people to take control of their data and to understand its value.”