Elon Musk is worried about the killer robots again. Getty Elon Musk has been ranting about killer robots again.

Musk posted a comment on the futurology site Edge.org, warning readers that developments in AI could bring about robots that may autonomously decide that it is sensible to start killing humans.

"The risk of something seriously dangerous happening is in the five year timeframe," Musk wrote.

Aware that internet commenters may mock him for his outlandish predictions, Musk defended his views, writing, "This is not a case of crying wolf about something I don't understand."

But minutes after he posted the comment, it was deleted.

The billionaire entrepreneur has made a habit of making apocalyptic comments about killer robots in recent interviews.

During a talk at a recent Vanity Fair conference, Musk warned the audience about killer robots. He suggested that advanced artificial intelligence could cause robots to delete humans like spam:

If its [function] is just something like getting rid of e-mail spam and it determines the best way of getting rid of spam is getting rid of humans ...

The interviewer went on to ask Musk whether humanity could use his SpaceX ships to escape killer robots if they took over Earth, but things don't look promising.

No — more likely than not that if there’s some ... apocalypse scenario, it may follow people from Earth.

Here's Musk's deleted comment from Edge.org:

The pace of progress in artificial intelligence (I'm not referring to narrow AI) is incredibly fast. Unless you have direct exposure to groups like Deepmind, you have no idea how fast-it is growing at a pace close to exponential. The risk of something seriously dangerous happening is in the five year timeframe. 10 years at most. This is not a case of crying wolf about something I don't understand.

I am not alone in thinking we should be worried. The leading AI companies have taken great steps to ensure safety. The recognize the danger, but believe that they can shape and control the digital superintelligences and prevent bad ones from escaping into the Internet. That remains to be seen...