By definition, spyware is any software that covertly gathers user information through the user's Internet connection without his/her knowledge. This type of software is generally used for advertising as is often included within freeware or shareware programs that are downloaded off the Internet. Some particularly mischievous spyware that exists on the Internet can be used to gather information about email addresses, the users’ activities on the Internet, and even passwords and credit card numbers. That information can then be passed along undetected to someone else. Some of the most common methods of receiving spyware is by installing some of the more common peer-to-peer file swapping products that are on the Internet today. This software runs as an independent program and can have the ability to monitor keystrokes, scan harddrives, read cookies, install other software and constantly relay information back and forth to the author of the spyware. This robs the user of memory resources on their computer and uses up bandwidth. It can make the host system unstable and cause system crashes. Often the freeware or shareware that is downloaded contains a licensing agreement for the use of the downloaded software. In many cases, this agreement indicates that the spyware will be installed along with the software. All too often this agreement is not read thoroughly or the language is buried inside carefully worded legal disclaimers. Once installed, the spyware monitors user activity on the Internet and transmits that information in the background to someone else. It is imperative to have a good anti-spyware installed on your PC. Even though, it has been proved after testing that the top anti-spyware can at the most detect 90% of the spyware and not cent percent, but its anyday better to take a risk of 10% rather than carry a 100% risk by not installing any anti-spyware on your system!