The message you are receiving is meant to inform you that someone may have made changes to or deleted the K9 log file stored on your computer.
Sometimes you will see this when someone has tried to access a blocked site but failed. The user then becomes concerned that the attempt was logged and tries to erase the specific log. The logs are stored on your computer and can be viewable only through the K9 Administration page within "View Internet Activity" but can be modified/deleted without the password by simply opening the log file on the computer and making changes. If this log is changed or deleted, some or all of the reports in "View Internet Activity" may no longer be viewable.
While it is possible to modify the log file without the password as it is stored locally on your computer, there would be no way to view the information as the log file is encrypted and the information stored in that file can only be viewed through the K9 Administration Page (which does require a password). Making arbitrary changes to the log file can "corrupt" some or all of the log data, meaning that some or all of the logs will no longer be seen in the "View Internet Activity" area of your K9 Administration page but because the file is encrypted, there would be no way of knowing what information to change to eliminate specific log entries.
However, keep in mind that I have noticed, on occasion, that this message appears even though no one has "tampered" with the log file.
If you continue to have issues with this or find it is impacting your K9 filtering service, contact K9 support by using Instant Support found at http://www2.nohold.net/noHoldCust31/Prod_16/KnowledgePortal/KPScripts//frameskp.asp?sid=162618&ds=nh21.nohold.net
After the third question, the answer should provide a link "Click Here to Email Support". This will redirect you to the K9 support form.
Hope this helps!