You may have seen in the news about another exposé about Yahoo being hacked, which is in addition to the previously disclosed 500 million email addresses hacked in 2014.  The new revelation (apparantely from 2013) cites 1 billion at risk email accounts that may have been compromised.

The problem potentially goes beyond those with Yahoo email account as Yahoo has managed (and possibly still does) BT email accounts and, as the name implies, Sky Yahoo Mail accounts are under Yahoo’s system.  

BT have advised all customers who haven’t changed their email password since August 2013 to change it now. If you have a btinternet.com email address you should have received an email from BT about this.  The details and instructions for changing passwords and security questions are available here: http://bt.custhelp.com/app/answers/detail/a_id/39411/c/7339

Sky hasn’t yet given any advice, but as the hacks are historical, it’s less likely that Sky emails are affected.