San Francisco, April 6 : As Facebook CEO Mark Zukerberg's phone number also emerged among the leaked data of 533 million Facebook users, a security expert has revealed that the Facebook CEO uses Signal. According to media reports, the leaked data includes Zukerberg's phone number, Facebook user ID, personal details like location, marriage details and birth date. "In another turn of events, Mark Zuckerberg also respects his own privacy, by using a chat app that has end-to-end encryption and isn't owned by @facebook," Dave Walker, a security expert wrote on Twitter. "This is the number associated with his account from the recent Facebook leak," Walker posted along with a screenshot of Zuckerberg's leaked phone number which mentioned, "Mark Zuckerberg is on Signal." Recently, personal data of nearly 53.3 crore Facebook users, including 61 lakh Indians, remerged online after a hacker posted the details on a digital forum. The easy availability of such data may make users more vulnerable to cybercrime, although Facebook has said that this is "old data". "All 533,000,000 Facebook records were just leaked for free. This means that if you have a Facebook account, it is extremely likely the phone number used for the account was leaked," tweeted Alon Gal, CTO of security firm Hudson Rock. The news of data leak was confirmed by Facebook to The Record. "This is old data that was previously reported on in 2019. We found and fixed this issue in August 2019," a Facebook spokesperson was quoted as saying in the report late Saturday. Recently, Signal became the fastest-growing app globally, including in India, both in downloads and monthly active users (MAUs) in the first quarter last year, according to data provided by app analytics firm App Annie. Signal is gaining immense popularity owing to its simplicity and focus on privacy. The upcoming privacy policy of Facebook-owned WhatsApp has actually helped Signal and Telegram grow their user base. Its controversial new terms of service will come into effect from May 2021. /IANS