Removing history

Using Aida32, I found a set of default urls under netscape history. They only cover 8/25/2003 from 7:55am to 8:48am. All the rest of the history is gone as it should be with my settings. Why are these the only ones here, and how do I get rid of them?
None of the other history for 8/25 or 8/26 or any time before that exists, only these. At the time that these occurred, I was and have been using Mozilla 1.4 as my default browser for over a two weeks now, and no history from this period exists.
Thanks
Wibur Huck