My mother uses Internet Explorer as her web browser. Some site she visited changed her search engine to something other than what she uses. Even if she types the URL into the address box, the browser is rerouted to this one search engine.
She dumped her cookies and her temporary Internet files, but the browser is still re-routed.
Usually those problems are solved by running a program such as AdAware (free download at www.lavasoftusa.com ) or SpyBot.
Those can also find and erase other spyware and unwanted stuff on your moms computer