What are porobots and spambots?
They are beings from the cyberworld (via viruses, worms and trojan horses) that are programmed to do things like register in forums that have low security, and post porn pictures with links to see more. If I lowered the security in this forum by not requiring folks to type the random looking letters at registration, and not requiring confirmation of registration by email, we would likely have a dozen posts by spambots and pornobots every day.
More on DoS and DDoS attacks here
http://en.wikipedia.org/wiki/Denial-of-service_attackMost spam like you receive every day, and DDoS attacks, are generated by high numbers of "zombie" computers, because if someone were to send it from one location their account would be suspended by their ISP. A zombie could be your or my computer if we have insufficient virus software. It invades your computer and sends out spam or porno without the owner even being aware. More on zombie computers here
http://en.wikipedia.org/wiki/Zombie_computerWe were subjects of DDoS attacks several times, but were finally left alone, once they realized that we couldn't suffer economically because we don't accept donations or have click ads and such. So there was no reason for the perpetrators to spend good money on an attack (these guys hold corporate sites hostage for ransoms like $25,000 and more) when it didn't cost us anything except a day or two downtime.
http://islamchristianforum.com/index.php?topic=695.0With the commerce website guys that have high transaction numbers (like L.L. Bean or somebody) they will simply shut down their site for a day. Then send an email asking how they liked it and if they want to be shut down some more. Then give details on where to wire the ransom to (Banks in Russia, Latvia etc.)