GAO and NIST determined the same thing.
The problems with the touch screen voting machines are numerous, but none of them are because they're hackable.
1) They are way too expensive, therefore too few will be available at precincts during heavy turout years.
2) They will for the most part be stored away for months, perhaps years at a time, then be expected to still function when the next election cycle comes around.
3) They leave smudges and fingerprints on the screen, which violates the spirit of a secret ballot.
Optically scanned ballots are scalable: You set up a few "suitcase tables" for small elections, and you set up many for heavy turnout elections, but in every case the precinct can be served by one scanner.
Optically scanned ballots leave an inherent paper trail for a manual recount.
Optically scanned ballots can be tabulated just as quickly as touch screen ballots, at a much lower cost.
The scanners are exercised every election, only the excess suitcase tables are stored for long periods between heavy turnout elections.