It is not an attack. It's an issue in the miner that doesn't handle large block efficiently. A fix is being tested. Both the stock miner and mikaelh's miner are impacted.
Looks like I "broke" Primecoin by accident. Oh crap.
Anything I can do to help fix this up? Might double spending the funds in smaller transactions help resolve this?
If so, what's the easiest way to do this, now that the offending TXNs are lingering around in my wallet?
Or can someone somehow just forcibly mine them to get rid of them?
Why aren't those TXNs being mined (but relayed) in the first place? I sent them with stock primecoind with stock fee settings. I feel like that really shouldn't happen...
How long are these going to float around in mempools if we don't do anything about it?
I assume things will temporarily fix themselves for now as soon as the last of these large transactions get encoded into the blockchain. And then soon there will probably be updated builds of primecoin that fix its handling of large transactions.