Following yesterday's failure, Twitter has gotten to the bottom of what went wrong: it was a software issue known as a "cascading bug".

If that doesn't mean an awful lot to you, you're not alone, so Twitter has tried its best to explain the issue on its blog:

A "cascading bug" is a bug with an effect that isn't confined to a particular software element, but rather its effect "cascades" into other elements as well. One of the characteristics of such a bug is that it can have a significant impact on all users, worldwide, which was the case today.

So nothing to do with a rash of people using aniated GIFs as avatars, then. Phew. [Twitter]