Millions of email accounts have been hacked leading to user details being shared online, according to reports.

Google Gmail, Yahoo Mail and Microsoft Hotmail are among the services said to be affected.

Hold Security said it had obtained more than 272 million accounts from the hackers, but it is not clear if the accounts have actually been breached.

Paul Fletcher, cyber security expert at security firm Alert Logic, said the best way for people to avoid being hacked was to regularly change their password.

He added: "Password management can be difficult for people trying to do the right thing and mix up their personal password usage, change them on a regular basis and be able to remember them.  

"My guess is that, 10-20 per cent of people care enough about security and password management to have any password strategy at all.

"The vast majority of internet users will only meet the minimum password requirement and try to use that password on all their systems."