Promoters of adware, software that shows advertising on a user's computer, use some cunning tricks to get you to install their software on your machine. Here's what to look out for.

Adware is, by definition, something reasonable people don't want on their computers. That's why malware can't just come out and ask people to install it. Often, the computer owner is completely unaware of it being installed. But not always.

When adware doesn't want to sneak in through an open window, it will try to trick you into letting it in through the front door. Don't think you could be tricked? Don't be so sure until you've checked out these most common ways people have been tricked into allowing malware to be installed on their machines.

Adware Installation Trick 1: Piggybacking

How it works: malware may come bundled with a legitimate piece of software the user actually wants, such as a game or emoticon. The malware is merely labeled "companion software," without any indication of what it will do.

How to fight it: be very suspicious of any software that comes bundled with other software. Don't installed software that comes bundled with other software unless you know everything that the bundled software does. After all, if the bundled program has anything to do with the program you actually want, why couldn't the software developer just get both programs' functionalities into a single piece of software? Software developers are now very sensitive to malware concerns and will provide a lengthy explanation of just why the bundled software is necessary, in the cases when they actually do need to use bundled software.

Adware Installation Trick 2: Bait and Switch

How it works: since people are getting more and more suspicious of bundled software, the malware's developers may simply label it as valuable software, for instance, a browser plugin that supposedly accelerates web browsing (but in reality only shows ads).

How to fight it: again, a suspicious mind is useful in avoiding malware. Ask yourself some questions:

o What will this software actually do? Malware often comes with very fuzzy claims attached. Sure, it says it will improve your browsing experience, but how? Often, this improved browsing experience just means a browsing experience with more advertising.

o If the software is so great, why is it being given away free? Most commonly, software is only given out free in two cases: if it's OpenSource (designed by a community of developers and not proprietary--OpenSource software is always clearly labeled as such)