Adware

Software that is used for the delivery of advertisements or webpages while the user is connected to or surfing the Internet.  The ads are usually triggered based on the user’s surfing habits.  For example, when the adware recognizes a user entering a search term it will display an advertisement relevant to that search term in hopes that the user will click on it.

Adware is installed in various ways.  One of the more common ways is by being bundled with other software, usually freeware or shareware.  When the user installs the freeware or shareware, they get a prompt instructing them that the adware will accompany the other software.  Since most people don’t pay attention to these install screens, the ad-ware gets installed without the person even knowing it.

Adware is annoying but not particularly dangerous.  It is usually installed in sneaky ways, but usually with permission of some sort.  It is used to deliver advertisements and pop-up windows to Internet users.  Sometimes they collect information on surfing habits but most adware companies operate advertising networks so their actions tend to be more business driven and less malicious than spyware.

Spyware

Spyware is nasty stuff.  Spyware is often used to leak private and personal information from your computer to someone who monitors and stores personal information.  Spyware is used to steal passwords, usernames, credit card info, surfing habits and more.  Information stolen by spyware can be used in credit card fraud, online banking fraud, identity theft and more.  Spyware is very different from adware because it’s primary purpose is not just to deliver advertisements, it exists to steal personal and private information.

Spyware is almost always forced onto your system without permission.  This is usually done by exploiting weaknesses in your operating system.  Spyware almost exclusively targets users of Microsoft Operating Systems and Microsoft Internet Explorer web browser.  By taking advantage of security holes in the MS Internet Explorer browser, spyware publishers can force their software onto your system with Active-X and other methods.