Actually, "an exchange made it look like someone bought a coin." https://willyreport.wordpress.com/

Bitcoin probably can't ever prevent good old insider manipulation, because every exchange affects every other exchange due to arbitrage. A price jump of $20 on BTC-e will swiftly travel to Bitstamp and everyone else. So if BTC-e decides to do something similar to what Mt. Gox did, there's nothing stopping them. All it takes is one shady popular exchange.

Bitcoin's dependency on exchanges is its greatest strength and weakness. Without exchanges, you probably wouldn't be able to sell bitcoins locally except in a sporadic way. There wouldn't really be an agreed-on price. But with exchanges, herd dynamics are always in full bloom, and you won't ever escape them.

EDIT: People buy and sell bitcoins at current market rate, and current market rate is defined by exchanges. That means if an exchange decides to make their own price artificially jump up, then everyone else's price will jump up too. That means bitcoin's price will be defined partly by whatever insider manipulation is going on at the time.