Update
Why has the hashrate dropped the past weeks?
It dropped in different few days. Some of them are internal hardware/network glitches, some of them are luck based. We haven't identified any form of DDOS attacks recently though.
It sounds really strange to me that at this stage of network growth there isn't a regular report of such attacks against ASICMiner or other entities. I expected many people buying up shares and then ddosing the competition.
If there was it would be pretty easy to prevent. Just don't ever have your mining farm ever talk to the outside world. Send everything through VPS running bitcoind as a relay.
Mining farm bitcoind ----> relay bitcoind ----> rest of world.
If things get real bad keep a dozen cheap VPS running bitcoind as an insurance policy. If a relay node goes down due to DDOS then the mining farm switches to the next one (or two) on it is round robin list. Given the low frequency of blocks (even 10% of the network is only a block every couple hours) it would take forever to find a DDOS all the relay nodes.