What exactly are they? What info can a Migra computer read from a foreign passport? If it is the info stored on the bottom of front page, then isn't it very easy for forgers just to alter it?

I am being curious for various reasons. Mainly, my credit card was hit for $27K in Asia for a BEER purchase!!! (Now, I love beer but not to that extent! ) The merchant had a copy of "my" UK(I do not hold one) passport with a valid Malaysia entry stamp...

So, what exactly do these computers display when our passports get swiped by customs?

Can these machines tell when info on the printed front page does not match the info stored on the bottom of the front page?