After a security breach. It looks like sombody just broke into wordpress development cycle and posted malicious code on the 2.1.1. From the wordpress blog:

Longer explanation: This morning we received a note to our security mailing address about unusual and highly exploitable code in WordPress. The issue was investigated, and it appeared that the 2.1.1 download had been modified from its original code. We took the website down immediately to investigate what happened.

As long as you upgrade to the new 2.1.2 version you should be on the stable side of the moon.

More on that on the official wordpress blog.