BT has pledged to contact broadband customers who might have been affected by a hack at Yahoo two years ago.
Yahoo revealed last week that it experienced a data breach back in 2014. BT has outsourced its webmail to the Canadian technology firm, which means millions of its customers could potentially have had their details compromised.
Speaking to the Guardian, a BT spokesperson said a minority of BT Broadband customers have a legacy email product from Yahoo.
However, the official did not say exactly how many people this concerns. Instead, the spokesperson confirmed BT "will be contacting affected customers specifically to help them keep their information safe".
BT has released a tool to allow anyone who is not sure whether or not they have a Yahoo webmail account to check.
The company has also recommended that customers make sure they reset their email passwords regularly.
News of Yahoo's data breach comes as TalkTalk seeks to recover lost ground after it fell victim to hackers.
In a trading statement, the company revealed that it lost 9,000 broadband customers between April and June 2016.