Did you already install SP1 for SharePoint 2013? If not, good for you! Microsoft found out some serious bugs within SP1 for SharePoint 2013 and is currently fixing them.​ As a prevention, Microsoft disabled download links for SP1 packages. In case that you already downloaded packages and waiting for the good moment to deploy them, just don’t!

“We have recently uncovered an issue with this Service Pack 1 package that may prevent customers who have Service Pack 1 from deploying future public or cumulative updates. As a precautionary measure, we have deactivated the download page until a new package is published.” – as found under http://support.microsoft.com/kb/2817429/en-us

As far as I know, no other functionality is affected other than installing post-SP1 PUs und CUs. I personally believe that Microsoft will sort this out in coming weeks. Stay tuned.