From an article at Microsoft Online Security:
Browser hijacking” is a type of online fraud. Scammers use malicious software to take control of your computer’s Internet browser and change how and what it displays when you’re surfing the web.
How do I combat online fraud?
If you keep your computer updated with the latest security software and updates, and practice safe Internet browsing you’re already doing a lot to keep the hijackers away.
But if your browser has already been “hijacked,” there are several ways you can combat online fraud and fix your browser.
How do I know if my browser has been hijacked?
- Home page or other settings change on your computer. Links are added that point to websites that you’d usually avoid.
- You can’t navigate to certain web pages, such as antispyware and other security software sites.
- A seemingly endless barrage of ads pops up on your screen.
- New toolbars or Favorites are installed that give you icons and links to web pages that you don’t want.
- Your computer runs sluggishly. Malicious software can slow down your computer.
For more information, see Fix your hijacked web browser.