Spyware and Adware are increasingly common and closely related forms of malicious software. Spyware refers to software that transmits personal information such as browsing habits without proper authorization. The functions of most advertising software (adware) can be classified as spyware, because they transmit information back to advertisers for marketing purposes. Adware refers to parasitic marketing software, which may be bundled with other seemingly desirable software, distributed by masquerading as a browser plugin, or more disturbingly, distributed via security holes in a user's browser. Beyond being an invasion of privacy and an annoyance to many users, spyware and adware programs are often poorly written, exposing victims to browser and operating system instability and insecurity, and often burrow deeply into critical operating system components making their removal a dangerous time consuming process.