3
What happens if someone maliciously decides to make squillions of transactions on the Bitcoin network?
I see there being two vulnerabilities. Firstly - computation resources used, though this doesn't seem to be a problem, at this stage, given the size of the mining pool.
But also - blowing out the size of the block chain. What if someone were to persist over a year of spamming transactions?
3
That's what transaction fees are for. You have to pay a fee for every transaction you want to have included in the block chain, especially if your transaction is for a small amount or if there are many transactions already waiting in the transaction pool.
Also, the size of Bitcoin blocks is limited. There is also a limit on the number of signature operations in a block. The most an attacker can do is to raise transaction fees.
1
Miners have the option to include or not include any given transaction in a block. If a particular account (or accounts) is attempting to make a large number of low-value transactions, miners could choose to not include transactions from that address in their blocks. Or, they could rate-limit senders of very small amounts.
1Note that having more transactions doesn't significantly increase the amount of computation required for mining. – Nate Eldredge – 2014-10-01T15:53:08.667