Some Paddy Power and Betfair customers have been warned to “remain vigilant” after a hack of up to 800,000 users.
A spokesperson for Flutter Entertainment, which owns the online gambling brands, confirmed to the BBC it had “suffered a data incident.”
Some personal information including IP addresses, email addresses, and online activity data has been compromised.
The company provided affected users with online safety information and told them: “There is nothing you need to do in response to this incident, however we recommend you remain vigilant.”
Flutter Entertainment has 4.2 million average monthly players across all its brands in the UK and Ireland.
Its other betting companies include Sky Bet and Tombola.
The company said the incident has now been contained and added: “No passwords, ID documents or usable card or payment details were impacted.”
However, cybersecurity experts have warned the breached data could be used to target unsuspecting customers with convincing personal emails in what’s known as a spear phishing attack.
Harley Morlet, chief marketing officer at Storm Guidance, said individuals that spend large amounts of money with these gambling companies could be targets.
“With the advent of AI, I think it would actually be very easy to build out a large-scale automated attack,” he told the BBC’s Today programme. “Basically, focusing on crafting messages that look appealing to those gamblers.”
Tim Rawlins, director and senior adviser at global security firm the NCC Group, told the BBC’s Wake Up to Money programme that customers should look out for detailed emails that might refer to their previous betting habits, encourage them to click links or give away credit card information.
“You might re-enter your credit card number, you might re-enter your bank account details, those are the sort of things people need to be on the look out for and be conscious of that sort of threat,” he said.
He added: “If it’s too good to be true, it probably is a fraudster who’s coming after your money.”
Mr Rawlins said his security firm has seen an increase in the quality of phishing emails and said AI is making it harder to tell a fraudulent email from a real message.