Spyware is a general term for software that installs on your computer, and collects personal information from you without your knowledge or permission. The information spyware collects can range from all the Web sites you visit to sensitive information including user names and passwords.
You could become vulnerable to spyware if you download executable files, or any type of software programs from unknown sources, such as websites you don't trust, by clicking on popup windows and installing browser components, or by executing email attachments.