DNS Redirection
Internet service providers (ISPs) such as Time Warner Cable and Optimum Online claim they're trying to help with DNS redirection, but the reality seems to come down to money. Domain Name System (DNS) redirection overrides your browser's normal behavior when you can't reach a webpage. Instead of displaying the normal 404 "File Not Found" error, the ISP sends you to a page of the ISP's choosing — usually a page full of paid advertising and links.
Innocent though that practice may be, computer viruses can do the same thing,
redirecting your browser to a hostile page the first time you misspell a domain. With ISPs, you can opt out of their DNS redirection (you'll find links below all the ads); with viruses, stay on your toes. Make sure you know what your browser's default 404 page looks like, and take action if you see anything different.