Outlook and Hotmail account holders were left vulnerable for almost three months after cyber criminals targeted Microsoft’s suite of email services boasting hundreds of millions of users.

A number of people had their accounts compromised in a breach that took place between January 1 and March 28, according to Microsoft.

Hackers broke into a customer support account, which then allowed them to gain unauthorised access to personal information, such as the subject lines of some emails, the identities of recipients of messages and the names of folders.

The company told affected users in an email that “the content of any emails or attachments” were not accessed in the breach earlier this year, and that it “immediately disabled the compromised credentials” once it became aware of the issue. Passwords were not stolen in the hack.

“We addressed this scheme, which affected a limited subset of consumer accounts, by disabling the compromised credentials and blocking the perpetrators access,” a Microsoft spokesperson said.

However, technology news site Motherboard reported that the extent of the breach was significant, with the content of some users' emails and inboxes being left exposed.

Microsoft confirmed that 6pc of the affected group could have been particularly vulnerable, with the cyber criminals potentially having “unauthorised access to the content of their email accounts”.