This spammer is quite annoying. He's started to spam 577 ltc transactions now. Due to the way we calculate priority, sending 577 coins (even with just 1 confirmation) makes it high priority enough that it can be done for free. And he's able to cram about 13 of these into each block for free:
http://blockexplorer.sytes.net/block/6a73e81f628fbd612c6c1359f7c7ef06dce074d1946608b51756d08ce7e95178There's only so much we can do about this since we can't really tell that these are spam transactions. The way to stop this is to require a transaction fee on all transactions, but I don't think we want to go that route. If you send a free transaction with higher priority, it will be include in the block before these spam transactions. Or if you want your transaction to always be include, just add a fee.
If this guy keeps sending 13 of these spam transactions per block, he will bloat the chain about 1.7mb/day. This might be something we just have to accept. This is the same way that Bitcoin works. If you have free transactions, there will be ways for malicious person to take advantage of it.
Though there is one solution I can think of. Which is to require a transaction fee on all coins sent that are not a day old. So if you try to send coins that are not a day old (i.e. don't have 576 confirmations), you need to pay 0.1 ltc fee. What do people think about that?