1. Spyware is OS dependent. Like Viruses, 95-99% of the people who develop them either a) don\'t think about Linux (BSD, Mac OS X, Solaris, etc), or b) are trying to point out (in the worst way) various security flaws in Windows that Microsoft hasn\'t fixed since they released WinNT or Win 3.0. Windows has enough security issues with it, and Microsoft has annoyed/frustrated enough of the programming/hacking community that makes it a very juicy target. And I don\'t see that changing any time soon.
2. Spyware can be installed through Internet Explorer if you aren\'t careful about how to handle installing programs from web sites. The fact that Internet Explorer doesn\'t have automatic & thorough pop-up window blocking doesn\'t help things either, as some pop-ups attempt to install things without you being aware. Sure, you can get external programs to help, but 9 times out of 10, the window has to open before it gets closed, and thus it\'s job is already done.
3. How do you detect if something\'s spyware? Well I can\'t really explain how I do it... It\'s more of a gut feeling, really. Partly I avoid downloading & installing little utilities, applications or games that are from companies or sites that don\'t look like they have a good reputation. \"Shareware\" and \"Freeware\" Windows programs are frequently spyware-designed any more. I\'ve been working with computers for so long any more, it\'s to the point of being as instinctual or natural for me to do that as it is to breathe.