BleepingComputer.com: Malware Variants?

Who creates these strains of Malware Viruses? is it one specfic group or are they sold to other people and modifed?
Anti-Virus Companies say some of these can steal Personal Infomation, set Keylogs and various other things like that.
But i have only ever found that RATs or actual Trojans do this.

Malwares business is now organized crime. Software programmers and hackers are hired by people to design such malwares. Malwares creations toolkits and services are available at a cost.

To have an idea read this paper by PandaLabs [PDF File] : http://www.pandasecurity.com/img/enc/Bolet...ndaLabs4_en.pdf
Goto section 6 in the report.

Thanks Romeo