DDoS

The reason for a DDoS botnet is usually either the wish to have enough firepower to virtually shoot people/sites/organizations off the net, or extortion, or a combination of both. The extortion of gambling websites before big sports events is just one example of many cases of extortion involving DDoS. The attacker usually takes the website down for a couple of hours to demonstrate his ability to do so whenever it pleases him, and sends a mail to the owner of the website, asking for money to keep the firepower away from his site. This sort of business model is well known for millenia, and merely found new applications online.