Microsoft founder Bill Gates says the cryptocurrency craze has “caused deaths in a fairly direct way”.

Gates said during a Reddit AMA (ask me anything) that digital coins were being used to buy drugs.

Whereas in the past drug users have had to pay using cash, cryptocurrencies allow the same anonymity while buying online, Gates explained.

“Right now cryptocurrencies are used for buying fentanyl and other drugs so it is a rare technology that has caused deaths in a fairly direct way,” he wrote.

Many experts have warned against investment in crypto without knowledge of the sector as the currencies’ market value is extremely volatile. Some have said that 2018 is the year of regulation around Initial Coin Offerings, while the UK government has launched an inquiry into cryptocurrencies and the underlying blockchain public ledger technology

“I think the speculative wave around ICOs and cryptocurrencies is super risky,” wrote Gates.

On blockchain, which has the capability to increase transparency in financial and other transactions, he continued: “The government’s ability to find money laundering and tax evasion and terrorist funding is a good thing.”

He was broadly positive about the direction of technology in general.

“Automation has been driving productivity ever since the industrial revolution including things like tractors and garment making,” he wrote.

“With software this will continue to accelerate so we need to think about how we educate people for the new jobs that will emerge.

“Overall automation is a great thing – eventually we won’t have to work as much but we are still at least a generation away from a big change there.”