Facebook's ongoing promises of online privacy took another hit overnight, as a software glitch led the social networking giant to reveal users' online chats.

Facebook was forced to deactivate the chat function once it was informed that the problem existed.

A bug allowed those who followed a series of steps in the newly-added 'preview my profile' feature to see private chats in progress and friend requests of those in their friends list.

This information is usually protected by users' personal privacy settings.

"Chat is unavailable as we work quickly to fix a bug reported to us," Facebook said in a blog post. "It should return to normal soon. Because of the bug, people could view friends' chat messages and friend requests for a limited amount of time if they manipulated the "preview my profile" feature in a specific way."

See how the exploit worked here.

Facebook has often fallen foul of privacy campaigners, most recently when four US senators took the company to task in a letter to CEO Mark Zuckerberg over changes to the site's functionality.

A survey by the Privacy Commission last week showed 45 per cent of New Zealanders have online profiles - mainly on Facebook, which claims to have over 400 million registered users worldwide.

Privacy Commissioner Marie Shroff said that 57 per cent of people believed that social networking sites were "mostly private spaces".

Interestingly, 88 per cent of people were still concerned about the sort of information that children revealed online.

Another survey by internet safety organisation Netsafe showed that 25 per cent of secondary school students said they had been aggressively sexually solicited online.