Where does Spyware/Malware come from?

Spyware/malware programs are authored by clever programmers, and then delivered to your computer through covert Internet installs. Usually, malware will piggyback on innocent-looking web page components and otherwise-benign software such as game demos, MP3 players, search toolbars, software, free subscriptions, and other things you download from the web. Subscribing to online services is especially bad for getting malware. In particular, whenever you sign up for a so-called "free" service or install new software, you must accept an "end user license agreement" (EULA). The fine print of the EULA will often include the phrase "the vendor is allowed to install third-party software on your computer". Since most users don't bother to read this EULA fine print, they naively click "accept", and install malware out of sheer ignorance.