Microsoft co-founder Bill Gates revealed what scares him about the advance of technology in an interview with Axios.

"There's always the question how much technology is empowering a small group of people to cause damage," Gates told the news site. "A small group can have an impact — in the case of nuclear [weapons], on millions; and in the case of bio[terror], on billions. That is scary to me."

He also issued a warning to tech companies, as the threat of government regulation hangs over Silicon Valley. "The companies need to be careful that they're not ... advocating things that would prevent government from being able to, under appropriate review, perform the type of functions that we've come to count on," he told Axios.

Tech giants Facebook, Apple and Alphabet's Google have come under growing criticism in recent months for what some see as a failure to self-regulate and mitigate the negative effects of technology on society.

Facebook and Google have struggled to keep inappropriate or hateful content off their sites, and Apple has clashed with law enforcement agencies over granting access to the personal data of suspected criminals stored on iPhones.

Gates attributed that to the companies' "enthusiasm about making financial transactions anonymous and invisible, and their view that even a clear mass-murdering criminal's communication should never be available to the government."

Read the full Axios interview here.