Admin Tools is reporting the availability of the yet-unreleased versions of Joomla! 2.5.12 and 3.1.2. Please note that these releases have NOT been officially published by Joomla!. Admin Tools is picking them up because these files are made available in JoomlaCode.org, the official Joomla! code repository, for testing reasons but without being hidden from the general public. Normally these files should only be visible to members of the Joomla! Bug Squad. Unfortunately for the first time in 3 years they were uploaded without any protection and for so long before a public release.
DO NOT INSTALL THOSE VERSIONS ON YOUR SITE UNTIL JOOMLA.ORG PUBLISHES A RELEASE ANNOUNCEMENT!
We are in contact with the package maintainer and we have reasons to suspect that the ZIP archiver on his Ubuntu box is acting up. Some update packages under some versions of PHP appear to be broken when using Admin Tools or the core Joomla! Update component (which is based on Admin Tools). We are working on a solution. We have also found some other issues with these packages so, please, whatever you do DO NOT INSTALL THEM ON YOUR SITES!
Troubleshooting / recovery instructions
If you have accidentally installed one of those two releases and the upgrade process failed halfway through you will need to restore from the backup you took immediately prior to upgrading Joomla!. If you do not have such a backup and have access to the back-end of your site, download and install (as you would install a component) the Joomla! 2.5.11 or 3.1.1 full update package depending on your Joomla! version. If you do not have access to your site's back-end, download that package file, extract it locally and upload all files to your site, overwriting existing files of the same name.
The future of the Joomla! update feature
The Joomla! update feature will be removed from Admin Tools in the upcoming 2.5.7 release. There were several reasons contributing to this decision.
For starters, Joomla! now ships with a core component called Joomla! Update. It is written by us and is merely an adaptation of Admin Tools' Joomla! update feature. The major differences are to be found in the way the component is finding and downloading updates. Admin Tools was reading the JoomlaCode.org pages for available releases. The Joomla! Update core component consults the official XML release file. The latter method is better as only officially published versions are listed, albeit a little slower to report an update since the time it's released. As for the download method, Admin Tools automatically uses curl or fopen() URL wrappers, depending on what's available. Joomla! Update only uses fopen() URL wrappers. Since the availability of the latter has become a necessity for Joomla! and many extensions to work properly there is no need to support both methods.
There are only two features found in Admin Tools' Joomla! update not found in the core component. The first one is the ability to take backups of your site before upgrading to the newer Joomla! version and the other is the ability to get an email to update your site with one click. When we built these features they were one of a kind. Nothing else offered remote one click updates with full site backups. In the last year we've seen the advent of services like Watchful, Admincredible and myJoomla which can do that and much more (using a copy of Akeeba Backup installed on your site as the backup engine, just like Admin Tools). So these unique features are no longer necessary.
As an extension to the previous reason, there is no reason for us maintaining the same code in two places. The Joomla! update feature was written in an era where Joomla! lacked this feature and we rushed to fill a usability gap, hoping that one day we'd be able to contribute the code back to the project. When Joomla! 1.6 was released we were unsatisfied with the update feature shipped with Joomla! and we continued developing our code. At some point we were able to include that code in Joomla!. We kept maintaining our code in Admin Tools in order to facilitate migration from Joomla! 1.6/1.7 to 2.5 and from old versions of 2.5 to newer versions of 2.5 or 3.x. Now we are well beyond the point that was necessary. It's time to let go of that code and let it live where it naturally belongs: the Joomla! CMS itself.
That said we might reconsider the one-click Joomla! update email feature in a future version of Admin Tools. Creating a plugin for just this feature isn't all that hard, but the decision will be ultimately based on our clients' feedback. If there is a demand for such a plugin we'll write it.