You would need a lot of coins but the way i think it would work is this:
Use mtgox since for the most part other exchanges follow gox.
1. Using half (or more) of your coins, sell out all the high bids you can at once. this will grow the gap between asks and bids.
2. at the same time, create an ask wall using the remainder of your coins at a penny above the highest bid you couldn't sell to. This will ensure that no transactions occur at a higher price than your artifically-created low.
3. auto-traders that haven't adjusted will eat away at this ask wall to some degree, which will make the buy and sell price basically identical.
4. Since all of the indicators look consistently bad, automated traders will adjust to this lower price, lowering their asks to below your wall to try to exit quickly. This is also when a lot of panicky weak hands will exit.
5. This is when you want to DoS the exchange. It's important to do this AFTER the price has adjusted, so that the outage creates more confusion and hysteria, but there is an overwhelming sense of a crash. If you can deface a site to report a wallet compromise, that's even better.
At this point, people should be desperate to get out at any price.
Buy a huge percentage of existing bitcoins and then sell each bitcoin for cheaper than you bought it for and cheaper than your previous sale. Given the entire currency is worth in the billions, nobody would do this, and there's nothing to gain from doing it.
Leak a rumor that there has been a fundamental vulnerability in it's crypto implementation and/or a fundamental problem in it's protocol that allows anyone to steal anyone else's funds and/or trivially mine bitcoins.
It'd have to look like a legitimate rumor, but this would work because speculators tend to easily spook (at least in other markets) and no one wants some anonymous internet person stealing all of their money.
Use mtgox since for the most part other exchanges follow gox.
1. Using half (or more) of your coins, sell out all the high bids you can at once. this will grow the gap between asks and bids.
2. at the same time, create an ask wall using the remainder of your coins at a penny above the highest bid you couldn't sell to. This will ensure that no transactions occur at a higher price than your artifically-created low.
3. auto-traders that haven't adjusted will eat away at this ask wall to some degree, which will make the buy and sell price basically identical.
4. Since all of the indicators look consistently bad, automated traders will adjust to this lower price, lowering their asks to below your wall to try to exit quickly. This is also when a lot of panicky weak hands will exit.
5. This is when you want to DoS the exchange. It's important to do this AFTER the price has adjusted, so that the outage creates more confusion and hysteria, but there is an overwhelming sense of a crash. If you can deface a site to report a wallet compromise, that's even better.
At this point, people should be desperate to get out at any price.