This was done by Anonymous (not the losers on 4chan, but the Insurgency, which is a raid site that tends to have much bigger plans and more dedicated people associated with it). Basically, they like to fuck things up because they think it's funny. Their plan was originally to spread the word about DMT and the Nexus. Obviously this would be terrible for us, because any publicity about drugs has to be negative in the public eye, and the last thing we want is negative publicity about DMT. They knew that it would really piss us off, and they think it's funny to piss people off. I think they decided to DDOS the site because they failed to spread a lot of publicity and had to go to plan b, which also made us pretty mad
(thankfully they didn't go through with plan a. That probably would have caused a massive public outcry about DMT, leading to a greatly increased effort by the DEA to crack down on DMT)