From a Facebook post by Jon Crowcroft:

So raspberry Pi ships with a) sshd on b) root login on sshd on c) the same default password on every Pi – doh! Do not plug in your pi to a net before changing at least one of the above, or you will, like a famous professor in the computer lab last week, get hacked, and deserve to be:)

Noted! (I’ve just ordered a new Raspberry Pi to replace the one that died on me.)

Footnote: the victim was not Jon!