Even if you have some of the best security in the world, if there is any unpatched vulnerability, it can present an opportunity for hackers, crackers, and website defacers. 
Microsoft Press site Hacked & Defaced http://www.neowin.net/comments.php?id=20516 Microsoft Press has been defaced this evening by a group named "Outlaw Group". Although the group doesn't seem to have caused much damage, this is clearly an embarassment for Microsoft.com webmasters. A clear example of where patches need to be applied.
Defaced MS Press Screenshot: http://www.neowin.net/staff/creamhackered/mspresshacked.png