During a scan, why did Acunetix WVS display a message window stating that URL rewrite was detected?

During a scan, Acunetix WVS displayed a message window stating that URL rewrite was detected. It gave me the options to abort and define the ruleset, or to carry on with the scan. What is this message about?

Answer:
URL rewrite (ex. mod_rewrite) is a common technology which is enabled on a web server (commonly APACHE) to change the format with which URLs are written.

Common example:
http://testasp.acunetix.com/showthread.asp?id=1

can be rewritten into:
http://testasp.acunetix.com/showthread.asp/id/1

?id=1 is a parameter input, however with URL rewrite it can be rewritten to /id/1 which looks like a directory structure. Acunetix is designed to display this message when it detects a file which resides in non-existent directory. When URL rewrite is enabled on the web server, Acunetix WVS must be configured to identify the ruleset which determines the rewrite structure, otherwise the crawler cannot correctly identify the site structure, and incorrect results will be reported.

It is possible to import the .htaccess or httpd.conf files into the URL rewrite node of the product settings to define the ruleset accordingly.

(See page 138 of the Acunetix WVS v5 user manual for more information)

If no URL rewrite is configured on your web server, just ignore the message and continue the scan.