Update2: Irrelevant. Pidgin/libpurple 2.4.3 quickly fixed the issue. Hurray to foss community! 🙂

Update: Seems like there'll be a new version soon. From #pidgin at irc.freenode.net:

There are issues with ICQ - ignore the message to upgrade and wait || We know pidgin.im is having difficulties

A few hours ago (01/Jul/2008 ~16:00 UTC) I tried connecting to ICQ using pidgin. Pidgin failed to connect and displayed the following error message:

The client version you are using is too old. Please upgrade at http://pidgin.im/

http://pidgin.im is down at the moment, probably because of the traffic this message caused 🙂

So, apparently ICQ have just changed the protocol with no backward compatibility, or at least blocked nonstandard clients. Or maybe it's just a temporary problem?

The only relevant post I've found so far is this Russian post.

I'll update this post when I hear something. Does it happen with other clients as well?