malware = refers to any and all of the following spyware = anything from cookies, to data miners, to keyloggers... adware = often goes hand in hand with spyware but is generally designed to generate revenue for the creator / distributor by showing you ads but doesn't necessarily mine your data trojan = aka a dropper or payload carrier. This is a type of virus that is self contained and usually carries a payload such as a worm or spyware... Here are some other types of malware classifications: Adware Appender Backdoor Blended threat Boot sector virus Bot Botnet Cavity filler Chain letter Clicker Companion virus Data diddler DDoS Dialler Dictionary attack Directory harvesting DoS Downloader Drive-by download Exploit File infector virus Fork bomb Hoax Intended virus Joke Keylogger Logic bomb Macro virus Malware Mass-mailer Metamorphic virus Mid-infector Misinfection Password stealer Pharming Polymorphic virus Prepender Ransomware Rootkit Smurf attack Spyware Trojan Virus Wabbit Worm Zip bomb Zombie http://www.virusbtn.com/Session-3c12aee55327f85ade46970f1b7dc989/resources/glossary/index http://www.symantec.com/business/security_response/glossary.jsp

I started writing this long answer until I saw well written descriptions at wikipedia.org http://en.wikipedia.org/wiki/Main_Page I recommend you read their pages on each term for a comprehensive description of each. They appear to have been written by folks who know what they're talking about and I would simply be repeating most of what they describe.