The Republican National Committee was not hacked because it had better defenses than the Democrats. Based on the fact that Russian hackers broke into the Democratic National Committee and roamed its computer network for months, collecting documents and emails, the D.N.C. That is not unusual — many government departments and many companies have been successfully hacked. And the Republican National Committee's own network does not appear to have been successfully hacked, suggesting that its defenses were stronger. that stored older material was successfully hacked, suggesting that its defenses were incomplete.

Source: New York Times January 11, 2017 16:39 UTC