Any software that covertly gathers user information through the user's Internet connection without his or her knowledge, usually for advertising purposes. Spyware applications are typically bundled as a hidden component of freeware or shareware programs that can be downloaded from the Internet. Once installed, the spyware monitors user activity on the Internet and transmits that information in the background to someone else. Spyware can also gather information about e-mail addresses and even passwords and credit card numbers, also called adware.
Programming code that was designed to do something usually counterproductive and occasionally destructive, whether through ignorance or malice. A virus makes copies of itself without any conscious human intervention. Some viruses do more than simply replicate themselves; they might display messages, install other software or files, delete software of files, etc. A virus requires the presence of some other program to replicate itself. Typically viruses spread by attaching themselves to programs and files. For example, the file formats for Microsoft word processor and spreadsheet programs allow the inclusion of programs called "macros" which can in some cases be a breeding ground for viruses.