.dat files are hidden internet files that store all of your surfing history
even if you delete the cookies and your history, if you have stuff on your
machine and do not want it to be retrieved you will have to delete the
index.dat files.

to do this boot into safe mode with command prompt then type this:
CD/ to get to the root directory
DEL Index.dat/s to delete the content of the files
shutdown -r to restart the computer after restart the files are still there but they are empty of all data.

Thats all i know on this subject later, happy tweeking.