It was recently announced that last February at least one hacker was able to gain access on one server at Harvard University potentially viewing private information on up to 10,000 grad students and applicants of the Graduate School of Arts and Sciences.
Zone-H(http://www.zone-h.org/content/view/14928/30/) has recently released a statistical breakdown of all the attacks from last three years. Surprisingly, Linux servers are the most attacked servers, even more than all version of windows combined. They suspect the reason for this is due to the fact that most server migrated to Linux, thus the attacks migrate too. I think this statistics is very interesting, because it really shows how “assets” comes into the play. It is not really the vulnerability or security weak spots within the operation system that draws most of the attack, but the assets guarded by them.