virtualbox.org

I noticed that there has been two release of VirtualBox-4.2.18 for Windows (and some other hosts)

VirtualBox-4.2.18-88781-Win.exe
VirtualBox-4.2.18-88780-Win.exe

The two files have identical content (thus signature dated Sept 6, 2013, 15:51:13, hashes..) and the about says version 4.2.18r88780 for both.

So why does VirtualBox-4.2.18-88781-Win.exe even exits?

Because some mirrors did not pick up the original update.