user9030: Someone could buy or mine bitcoins, and send them in small transactions all day to spam the blockchain.
Is this possible? And could this mean the end of the trust people have in bitcoin?
edit:
And what if someone makes bigger than 0.01 BTC transactions from one of his address to another all day. Making thousands of meaningless transactions, those totally spamming the blockchain. That wouldn't even cost much I believe. Is this possible?

user26344: You can create unlimited addresses and then send amounts of bitcoins which are over the fee-less minimum transaction limit to your own addresses.  That means you can technically spam the blockchain for the price of the electricity. 
A transaction may be safely sent without fees if these conditions are met:

It is smaller than 1,000 bytes.
All outputs are 0.01 BTC or larger.
Its priority is large enough (see the Technical Info section below)

https://en.bitcoin.it/wiki/Transaction_fees
Anyone know how the bitcoin core could stop you from doing that without blocking your IP from the network??  Even in that case, all you need to do is spoof your IP address over and over again>>> 

user-1: Yes, it is possible, and called transaction spamming. If you consider it cost effective spamming probably depends on how much it is worth to you to bloat the blockchain, already at a size measured in double-digit GBs, for everybody who keeps a complete copy!
However, there are some possible mitigations already implemented. First of all, many clients delay forwarding very small transactions and delay incorporating them into blocks or even require a transaction fee for them. As the transaction spam problem becomes larger, surely more mining pools will stop bothering unless a transaction fee is included.
Finally it is not strictly necessary for every single client to keep every single block of the blockchain around. Hence the long-term impact of such spamming is probably rather limited, and its widespread implementation, if not now then at least sooner or later, costly.

user5757: Such transactions will be subject to fees.  You can read about the fee schedule here.  The fees apply if the transactions send a small amount of coins, or send the same coins over and over (giving the transactions a low priority score).  
The fee is set at BTC 0.0001 per 1000 bytes.  Thus someone who wants to spam the block chain with 10 MB will have to pay at least BTC 1 in fees.  That's about US$500 at today's prices, and it causes the block chain to increase in size by about 0.1%, which nobody will probably even notice.  If you're going to spend $500 on mischief, you'll get a lot more bang for the buck by spending it on eggs and toilet paper!

9030: <p>Someone could buy or mine bitcoins, and send them in small transactions all day to spam the blockchain.</p>

<p>Is this possible? And could this mean the end of the trust people have in bitcoin?</p>

<p>edit:</p>

<p>And what if someone makes bigger than 0.01 BTC transactions from one of his address to another all day. Making thousands of meaningless transactions, those totally spamming the blockchain. That wouldn't even cost much I believe. Is this possible?</p>
 26344: <p>You can create unlimited addresses and then send amounts of bitcoins which are over the fee-less minimum transaction limit to your own addresses.  That means you can technically spam the blockchain for the price of the electricity. </p>

<p>A transaction may be safely sent without fees if these conditions are met:</p>

<ul>
<li>It is smaller than 1,000 bytes.</li>
<li>All outputs are 0.01 BTC or larger.</li>
<li>Its priority is large enough (see the Technical Info section below)</li>
</ul>

<p><a href="https://en.bitcoin.it/wiki/Transaction_fees" rel="nofollow">https://en.bitcoin.it/wiki/Transaction_fees</a></p>

<p>Anyone know how the bitcoin core could stop you from doing that without blocking your IP from the network??  Even in that case, all you need to do is spoof your IP address over and over again>>> </p>
 -1: <p>Yes, it is possible, and called transaction spamming. If you consider it cost effective spamming probably depends on how much it is worth to you to bloat the blockchain, already at a size measured in double-digit GBs, for everybody who keeps a complete copy!</p>

<p>However, there are some possible mitigations already implemented. First of all, many clients delay forwarding very small transactions and delay incorporating them into blocks or even require a transaction fee for them. As the transaction spam problem becomes larger, surely more mining pools will stop bothering unless a transaction fee is included.</p>

<p>Finally it is not strictly necessary for every single client to keep every single block of the blockchain around. Hence the long-term impact of such spamming is probably rather limited, and its widespread implementation, if not now then at least sooner or later, costly.</p>
 5757: <p>Such transactions will be subject to fees.  You can read about the fee schedule <a href="https://en.bitcoin.it/wiki/Transaction_fees">here</a>.  The fees apply if the transactions send a small amount of coins, or send the same coins over and over (giving the transactions a low priority score).  </p>

<p>The fee is set at BTC 0.0001 per 1000 bytes.  Thus someone who wants to spam the block chain with 10 MB will have to pay at least BTC 1 in fees.  That's about US$500 at today's prices, and it causes the block chain to increase in size by about 0.1%, which nobody will probably even notice.  If you're going to spend $500 on mischief, you'll get a lot more bang for the buck by spending it on eggs and toilet paper!</p>
