Microsoft has admitted that hackers had access to some of its Outlook, Hotmail and MSN email accounts for at least three months.
The software company would not say how many accounts were compromised in the breach that lasted from 1 January to 28 March.
Hackers stole login credentials for a Microsoft customer support agent and were able to access people’s emails and read subject lines, folder names and other email addresses.
A Microsoft spokesperson said: “We addressed this scheme, which affected a limited subset of consumer accounts, by disabling the compromised credentials and blocking the perpetrators’ access.”
The company said the hackers would not have been able to access the email content of the majority of users affected.
However, it said a small group of less than six per cent of those affected was provided with additional support as their emails could have been accessed.