user6284: 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?

user11253: 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.

user19476: 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.

6284: <p>What happens if someone maliciously decides to make squillions of transactions on the Bitcoin network? </p>

<p>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. </p>

<p>But also - blowing out the size of the block chain. What if someone were to persist over a year of spamming transactions?</p>
 11253: <p>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.</p>
 19476: <p>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.</p>

<p>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.</p>
