This isn't like the ones who DDOS'ed MS out of their hatred for it or the ones who blackmailed & DDOS'ed a gambling website when they refused to pay up.
I severely doubt this line of thought.. but they didn't make any friends with their "switch from X to us" campaign, and it only takes one bruised ego with a lack of ethics to stir up trouble.
That said, if it's like most other DDOS attacks I've seen reported, the target is probably a user of the service with Posterous merely being unlucky enough to host a particular site someone doesn't like. I vaguely recall another platform got DDOSed recently due to some Israel vs Iran type cyberwar.
Weebly said (I think in their YC Founders at Work interview) that they get multiple DDoSes a day, aimed not at them but at sites they host. Now they have good enough systems in place to deal with it that they said they often just don't notice.
I guess when you host enough people's content, it's only a matter of time before someone wants to DoS something you're hosting.
Maybe, and take it with a grain of salt, some people got infuriated by their recent switch to posterous campaign. I know this may be a very remote option, but in my opinion it's very possible.
The botnet controller could be extorting websites directly... wire $5000 to my paypal account or your website will go down. Anyone from Posterous care to confirm/deny in this case?
It's not uncommon. There was an article a long time ago telling the story of a DDOS attack on a gambling website, and how a guy who was a philosophy major (iirc) figured out how to beat it, and then formed a company providing the same service. Forgot the url/title/etc, but it was good. Plenty more available with a search.
This isn't like the ones who DDOS'ed MS out of their hatred for it or the ones who blackmailed & DDOS'ed a gambling website when they refused to pay up.