Even hand-count isn't foolproof
Bleh. Watch the 2006 Mexico Elections to see how even hand-counting can be botched if the system allows it. The counting process is like this:
1) Each polling station counts the votes,
2) Results are jotted down on an official act,
3) Same results are posted outside the polling station,
4) all ballots are put into sealed envelopes, put into a package that itself is sealed,
5) the act is put in front of said package.
Then the "district counting" consists in basically feeding the numbers on these acts to the central counting system, and the ballots are never, ever touched again. The pretext on the last election was that "opening the packages was illegal and useless".
Now anyone can see that the act could have been tampered with, and in fact, in some cases this was proven: the "outside polling station" sign and the act had, in some cases, 200 or 300 count "errors". Yet most of these were not even checked, even during the "recount" (which only recounted 9%, and didn't even open most of the packages).
E-voting only does the process easier, but the 2006 Mexico elections prove that even the manual system is fraud-prone.