The machines that were hacked, were not protected by sophisticated software. Go to any high school and you find kids who can do this kind of hacking in their sleep and you can probably find at least one that can hack many of the most secure government or big business computers.
Every month or two we see a major story of a federal agency being hacked, usually just for the ‘fun’ of it.
Another factor are the statements from WikiLeaks founder, Julian Assange. No matter what your personal opinion of Assange (for the record, I think that he is an asshole who most likely caused the death of people by exposing their names and has even endangered international relations and security) he has never released data that has been proven to be false nor has he been proven to have lied where WikiLeaks is concerned. Mr. Assange has repeatedly stated that data did not come from the Russians. He has in fact, eluded that the files were supplied by a member of the DNC