There was a company which used to make hard drives for the military (perhaps they still do, but nothing on Google) which had a physical pull tab on the back which released an acid into the drive enclosure. Anyone remember this? I read about it perhaps 10 years ago.

Was it an acid? I've heard of thermite or magnesium. Same idea though

I assume was something like acid since it released a liquid into the cavity.

Sounds vaguely familiar to me too.

... and not by malware :-)

Definitely something you want to trigger by physical contact, not pure software.