Edward Snowden took to Twitter to voice his opinion on two of the world’s top cryptocurrencies.

Both Zcash and Monero claim to be different than other cryptocurrencies by providing users with more secure and completely anonymous transactions.

It might be the reason Snowden, a world-famous advocate for user data security and anonymity, would choose these two digital currencies specifically to venture an opinion on.

On Twitter, a user @masonic_tweets remarked, “Zcash is the only altcoin (that I know of) designed and built by professional and academic cryptographers. Hard to ignore.”

In response, the former Central Intelligence Agency employee wrote, “Agree. Zcash's privacy tech makes it the most interesting Bitcoin alternative. Bitcoin is great, but "if it's not private, it's not safe."

Agree. Zcash's privacy tech makes it the most interesting Bitcoin alternative. Bitcoin is great, but "if it's not private, it's not safe." https://t.co/HqwQOvSCiz — Edward Snowden (@Snowden) September 28, 2017

He also commented on Monero, a supposedly untraceable cryptocurrency that contain privacy mechanisms, but which reported a bug earlier this year.

A statement from developers on the bug read, “it allows for the creation of an unlimited number of coins in a way that is undetectable to an observer unless they know about the fatal flaw and can search for it.”

Snowden replied that Monero is a “great project” pointing out that “the problem with amateur crypto is mistakes happen and have huge consequences for people like me.”

This is also in reference to findings published on MoneroLink that suggest as much as 60 percent of Monero transactions can be linked, meaning that transactions are not as anonymous as users would have initially hoped.