How do I prevent unauthorized editing of my webpage. I recently noticed that a few words on my web page had been turned into links to someone else's website. I looked at my markup expecting to see changes made to it but I didn't see
any. Thanks in advance for your help.
If your website is hosted on a free service, the service is probably inserting advertising into your webpages. That's how they make money.
If your site is hosted on a conventional hosting service that you pay for, then it sounds like your site may have been hacked. Google has just posted a lot of good advice on what to do when your site has been hacked on YouTube and their Webmaster blog. A quick search should get you some good advice.