Yep. Some viruses that infect other programs don't really care what the other program is, and will infect it anyway if possible.
nah
I don't know what virus produce viruses, but a virus called "Downloder" can downlode viruses from Google, bing ...
Viruses are normally found online, through downloads.
The things commonly considered to be viruses are typically malware. Viruses and such are written to either be malicious in nature, or retrieve data from the infected node, thus distributing that...