Only December the 2nd and we already have 2 new releases this month! It may seem as we can't get enough releases out the door. But these ones are for your security, so...
It is extremely strongly advised you upgrade!
These releases patch the security issue discovered this week in 1.x releases. (If you are running version 0.9.1 or 0.9.2 you are not affected, but it would still be a good idea to upgrade.)
Those versions are codenamed after Anne & Chris who were the first two users reporting the issue. Thanks to both of you as well as to all other users who have helped identifying and fixing this issue in such a short delay.
These versions also include additional security measures, just in case. Sort of having two locks on your door instead of one.
Bonus in version 1.8.6 "Anne": Yearly archives are back. You can display all posts for 2005 with your-blog-url?m=2005
Bonus in version 1.9.1-beta "Chris": a few little bug fixes that make this version less of a beta than 1.9.0