Just out of curiosity: How does Hardware killer Malware work?

First of all I want to say I love you all here at MajorGeeks, w00t!! Thank you for helping me to find real time anti malware scanners that work! These things have saved me alot of trouble already. And to show my appreciation, I'm getting you all pizza and soda! :XD


Though I'm curious how do Hardware killers like the Malware that kills BiOS and destroys Hard Drive Controllers (had that happen to be once several years ago) work? Are they files that need to be downloaded and then opened? Do they auto activate upon visiting a site? And is there any delay between the infection time and they do their damage?

Also what exactly is a decompression bomb it never gets counted as a infected file and I've even seen a few legit Windows files marked as such. I read somewhere it is a file that compressed in a weird way and due to the way it's compressed would eat up my system resources then it should.