spamming (sending millions of transactions of 1 satoshi, etc).
The dust threshold was introduced in 0.8.2 and was set at 5430 satoshi.
https://bitcointalksearch.org/topic/bitcoin-qt-bitcoind-082-final-available-219504
Fee Policy changes
The default fee for low-priority transactions is lowered from 0.0005 BTC
(for each 1,000 bytes in the transaction; an average transaction is
about 500 bytes) to 0.0001 BTC.
Payments (transaction outputs) of 0.543 times the minimum relay fee
(0.00005430 BTC) are now considered 'non-standard', because storing them
costs the network more than they are worth and spending them will usually
cost their owner more in transaction fees than they are worth.
Anyone knows whether the threshold has been changed after the min relay fee has been dropped in 0.9.0?