The headline-grabbing tale of an Italian man who said he was kidnapped and tortured for weeks inside an upscale Manhattan townhouse by captors seeking his bitcoin highlights a dark corner of the cryptocurrency world: the threat of violence by thieves seeking digital assets.

The alleged attempted robbery is known as a “wrench attack.” It’s a name popularized by an online comic that mocked how easily high-tech security can be undone by hitting someone with a wrench until they give up passwords.