Personal details including phone numbers of 533 million Facebook users have been leaked and posted on a "low-level" online hacking forum.

The latest data privacy leak from a Big Tech firm affected users from 106 countries, including 32 million in the US, 11 million in the UK and 6 million in India. Data leaked included phone numbers, Facebook IDs, full names, locations, dates of birth, profile biographies, and in some instances their email addresses.

Facebook's director of communications Liz Shepherd claimed the data was stolen two years ago, adding that the company "found and fixed this issue back then.

But Alon Gal, chief technical officer of cybercrime intelligence firm Hudson Rock which detected the leak on Saturday, told the Business Insider the information could be used by online fraudsters for identity theft or phishing scams.

"A database of that size containing the private information such as phone numbers of a lot of Facebook's users would certainly lead to bad actors taking advantage of the data to perform social engineering attacks [or] hacking attempts," Gal said.

Reports emerged in January of an online bot offering users' data for cash, but now the entire cache of details has been dumped on the internet for anyone to misuse

"Individuals signing up to a reputable company like Facebook are trusting them with their data and Facebook [is] supposed to treat the data with utmost respect," Gal added. "Users having their personal information leaked is a huge breach of trust and should be handled accordingly."

User confidence in Facebook and its empire of social media sites and apps is already low. In January millions ditched mobile phone app WhatsApp for its Russian-developed rival Telegram over new terms and conditions under which users had to agree to their data being shared with Facebook to help it sell targeted advertising.