Software forced onto the unsuspecting masses to combat
Viruses. Usually written by ex-virus writters who needed a steady income.
Differs from
viruses in intent, and cost. Viruses are usually free, whereas anti-viruses are not. Anti-virus software also tends to have a flashier interface.
Both software types will severely impact your ability to do anything productive, both will occasionally greet the users with unwanted
popups, add web tool bars, provide inaccurate (but sponsered) search results, and keep your local IT shop in business.