property HistoryFilename: string;

HistoryFilename is a String property used to identify the file name for saving and/or restoring the IP addresses in IPHistoryList. The default value for HistoryFilename is defined in the constant IP_WATCH_HIST_FILENAME. 

HistoryFilename is used read previous IP addresses into IPHistoryList in the LoadHistory method. HistoryFilename is also used to store IP addresses, when HistoryEnabled is True, in the SaveHistory method.