I'm not sure if El has conclusive evidence yet, but most things point(ed) to an attack.
There was a massive spike in connections, a massive drop in poolspeed, a massive increase in idle miner and rpc coms for everyone.
El has gone to bed for the night it would seem, but before he left, he tweaked the iptables to be a bit more restrictive (which appeared to help for a bit, but wasn't an end all solution) and implemented better more specific logging techniques to further investigate over night behavior when he can tomorow.

While im sure the idle miners and rpc coms are annoying, i have to point out at least the server has stayed up through this (possible)attack. That's pretty awesome in it's own. That's a bit more than other pools can say about some of their more recent attacks. Not only has it stayed up, but our luck hasn't been too shabby through it either