Spam:
Used because 'Spam' the product is of poor quality compared with Ham and is not the real thing, hence 'got nothing to do with the original', leaves a bad taste in your mouth, hence 'in bad taste' and during the second world war it was known as 'tinned c**p', and because the troops got fed up eating it and wanted real Ham, hence, get back on track'.
I found this out doing a google search when I wanted to know what computer 'Spam' meant.