This morning we were made aware of an internet-wide security vulnerability with the Open-SSL framework, known as Heartbleed, that is also used by Wunderlist. In order to keep your data safe, we pre-emptively turned our Sync Service off to eliminate any potential security breaches.
We are currently working with our partners at Amazon Web Services to eliminate the potential security vulnerability as fast as we can. During this time, the majority of Wunderlist services will be unavailable (including Sync, Log In/Sign Up, Reminders, Mail to Wunderlist etc.). We do apologize for this and will be posting regular updates via @WunderlistHelp on Twitter and on our status page http://status.wunderlist.com/
You can find out more information about Heartbleed at www.heartbleed.com