Hey MASSAMIGAN. First off, Welcome to Amiga.org :-D
As to your question, people who write 'malware' (generic term that covers Trojans, adware, spyware, and virii) want to do as much damage as possible, so they target the most popular systems.... any Windows machine is a prime target, or course. Amiga's are largely immune, BUT you do want at least a basic Virus checker on your Amiga, I don' think they are many 'current' virii on Amiga, but you still may run into one on an old disk, etc.
