To do a true online search for your key-words, you need to use a computer that has never visited your web site. Or use tools that will show your page rank and placement in the big search engines. Using your own PC will produce a "tainted" search. Every time you visit a web site small snippets of information are stored on your computer called "cookies". This enables your machine to pull up the page faster. Most cookies are not harmful to your computer, They actually enhance your online browsing experience. If you do visit a page that gives a warning, it is usually best to avoid it.
All the big search engines like Google, Bing, and Yahoo usually scan for malicious code. They do not want their visitors to catch a "bug" as it can quickly spread and cause many problems. The internet has been brought down a couple of times by a mean virus. Large corporations have been attacked in this way also. Usually a malicious code is attached to a file and when opened it spreads to every computer on the net work.
Even signing out of your favorite homepage will usually produce different results when doing an online search. Deleting your temporary files can help your computer to run smoother and quicker when you browse or "surf" online, files are saved in your cache. Depending on the computer and cache storage size determines how fast your cache storage will fill up. Sometimes your computer will "bog" down because your cache is full. Deleting temporary files will not cause you to loose email or saved programs. You might need to enter passwords again though. You can set up your computer to delete temporary files on exit from the browser. You can find the settings in your options and advanced settings.
Cookies are generally not harmful to your PC. Using an online antivirus will give you some protection from "bugs". If you need an antivirus program, free programs are available at BugGenius.com If you have an online business I recommend using a paid program. Most free antivirus are fine for basic home computing.
"Some cookies are better than others"