The most dangerous living beings in history have killed billions between them. Mostly that's diseases, but we can also easily add tens to hundreds of millions from humans fighting and starving each other over the last 200 years alone. Currently around a million a year killed in road traffic accidents, too, but I don't see stats for the total worldwide deaths since their invention.
The greatest threats from other computer programs have been that during the Cold War the NATO early warning radar triggered an alert for a massive incoming fleet of Soviet aircraft because it hadn't been programmed to know that the moon wasn't supposed to respond to IFF pings, while the Soviet early warning radar triggered an alert an incoming ICBM because it hadn't been programmed to correctly handle the sun reflecting off clouds. It was human intervention which stopped that turning into a pointless self-annihilation, and that's specifically what gets lost as automation increases.
I also do not believe that either of these threat models "are very thoroughly known and understood", because if the former was then we would've seen an end to genocides, while if the latter was we would've seen an end to zero-day vulnerabilities (especially in critical infrastructure).
The greatest threats from other computer programs have been that during the Cold War the NATO early warning radar triggered an alert for a massive incoming fleet of Soviet aircraft because it hadn't been programmed to know that the moon wasn't supposed to respond to IFF pings, while the Soviet early warning radar triggered an alert an incoming ICBM because it hadn't been programmed to correctly handle the sun reflecting off clouds. It was human intervention which stopped that turning into a pointless self-annihilation, and that's specifically what gets lost as automation increases.
I also do not believe that either of these threat models "are very thoroughly known and understood", because if the former was then we would've seen an end to genocides, while if the latter was we would've seen an end to zero-day vulnerabilities (especially in critical infrastructure).