BT is advising all customers still using the old Yahoo Mail-based version of BT Mail to change passwords in the wake of yet another Yahoo hack.

While BT ditched Yahoo Mail for Critical Path (now owned by Openwave Messaging) back in 2013, some customers on older legacy services still using the old Yahoo-based service may still be at risk.

BT and Yahoo have yet to identify if any customers using the old platform are at risk, but is nonetheless still advising customers to change passwords and remain vigilant.

A BT spokesperson told PC Mag: “Following Yahoo's previous announcement in September [see here] we have already assisted BT customers who have our legacy Yahoo email product to protect their information by resetting their passwords.

“We are working with Yahoo to understand any further implications from this new announcement for BT customers and will take any additional steps necessary to help our customers stay secure. We recommend customers regularly reset their passwords and in particular anyone who has not changed their password since 2013 to do so immediately.”

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Sky, which announced a move to Yahoo Mail back in February 2013, has yet to respond to our inquiries or issue a statement on the latest development.

In better news for Sky customers, PC Mag was recently able to confirm that customers migrated to Sky’s network when it bought O2 Broadband back in 2013 are safe from a TalkTalk-style backdoor intrusion.

Update: While sources have been unable to confirm the number of Sky customers affected, PC Mag understands that it is significantly less than the millions of Sky customers who use Yahoo Mail. It’s also understood that any affected customers would be contacted individually.

Sky spokespeople have issued a statement: “Sky takes the security of our customers’ data and information extremely seriously. Overnight Yahoo announced that certain user account information was stolen from its network in 2013.

“Yahoo is the provider of Sky.com email accounts. In line with their advice, we are encouraging Sky.com email holders to change their passwords and security questions.”