[redfast00]

Voltage injection is (IMO) the easiest attack. There's also optical fault injection, where you remove the black encapsulation from the chip and hit the bare die with a laser (that sounds really difficult though).

On some chips, you can drill into the black encapsulation and find testpads that are not connected to pins on the IC. This is sometimes used for smartphone unlocking.

Edit: Thanks for the compliment by the way, it really made my day that I got someone interested in hardware hacking