For the past several hours, the Messenger servers have been showing the majority of contacts offline. You can however still talk to contacts using offline message. There were other similar issues earlier on in the day and the problem just seems to have progressively gotten worse.
This isn’t a new problem either. Messenger has continually had these problems on and off for several months now.
If you use the Messenger web-based client within Hotmail, or clients which use the older protocol versions (like Windows Messenger on XP), you may get slightly better results, however for the most part there isn’t a lot you can do about it except wait for it to be corrected.
Wolfgang Hoelzel from Microsoft Germany stated:
We are currently investigating the cause of the problem internally.