A very large portion of v2 hashing is offline (btcguild - roughly 30-40%; for nearly 3 hours now) and a couple of v1 miners got lucky in a row.
The rest of the v2 network overtook them and the network reorganized.
Only about 3 TH/s of BTC Guild was offline. The DDoS was only affecting getwork and a few people using the very first versions of Stratum which couldn't connect properly without being redirected from getwork.