It seems that Lindenlab introduced today a new version of their ToS according to their blog. This means, if you want to continue to play SL you need to agree after the next login in the client to them. There should be a dialogue box with the new ToS in it and you can either agree or disagree.
Well, in reality the dialogue box on my client looked like that:
This is something that shouldn't happen. I could have agreed to it that way. After a restart the client showed the new ToS correct.