DNS lookup information expires after N days:

After the specified number of days passes since the lookup was performed, the program will try to resolve the IP address again.

Number of threads used during lookup:

The default number of threads is 50. Increasing this number may accelerate the lookup process in some cases.

Some DNS servers cannot handle large number of DNS requests which causes for some resolvable IP addresses not to be resolved. If such problem occurs, you can decrease the number of DNS threads, clear the DNS cache and perform the analysis once again.

Ask for confirmation before analyzing profiles with DNS lookup ON:

This option may be useful because you must be connected to Internet while resolving IP addresses so the program will remind you of that.

Clear DNS Cache:

Use this button to clear the program's DNS cache.