If your computer is suddenly acting oddly, sending you to porn or other worthless sites without explanation, replacing the links you had saved in your bookmarks, or adding pop-up ads to every page you visit, then you probably have what is widely called "spyware", "adware", or "malware." In short, you have a problem.
Run Anti-Malware Programs
There is no single perfect solution, but there are some steps you can take. For a free spyware-killing program, try Ad Aware. Though it is imperfect, it is widely used and could help solve your troubles.
After you've followed the instructions for Ad Aware, follow up with a round of Microsoft AntiSpyware. That program will remain free until summer 2005, after which it will become a paid application.
If you want to be extremely thorough, also try Spybot: Search and Destroy and SpywareBlaster. Fair warning: There may be some conflicts if you run all of these programs, since some malware-removal tools will recognize others as being malware themselves. But if your problem won't go away, it can't hurt to try a couple of different programs.
Think Twice About Opening E-Mail
Some malware is passed on via e-mail. As a rule of thumb, NEVER open any file attachments unless it's a picture, a video, or a file that you specifically requested. There is no such thing as a file that opens up some kind of special message after you forward it a certain number of times. No, you will not get free stuff because you forward an e-mail to your fifty closest friends, nor will sending a message open a video file. New e-mail users should learn this one lesson and learn it well: NEVER forward chain e-mail. Most forwards are hoaxes and a waste of time.
Most likely, though, the malware landed on your computer by your perfectly innocent use of the Internet. If someone in your household was searching for something and just happened to have landed on the wrong page, they might have accidentally picked up malware.
Get a New Browser
The best line of defense against malware is to do the following: