It sems that this kind of vote changing has been discovered in Illinois, Maryland and Rhode Island. Where lese is this happening. One commenter describes this as a 'calibration error', as do the election officials, and he claims that there are examples of this happening in both directions R-->D AND D-->R. However, all examples of which I have heard are all in one direction, R-->D.
Lesson to be learned, watch very carefully when you vote and bring ANY discrepancies to the attention of the officials AND stick around to make sure that they take action. Be sure they do not put the fraud machine back into operation as soon as you leave.
And as the article states, one major requirement should be the printing of a copy of the votes cast, with one copy for the voter and one copy being retained for possible recounts (especially in the case of obvious discrepancies in totals)
Blatant Vote Fraud Via Rigged Machines in Illinois - YouTube