Those who use Acunetix Web Vulnerability Scanner are bound by the Acunetix End User License Agreement (EULA) and can only scan designated sites with permission to do so. If you are receiving a notification that “This site was scanned by someone using Acunetix Web Vulnerability Scanner.” the scan was NOT performed by Acunetix Ltd but by a user using our tool.
If you did not authorize a scan then you should check the source IP of the scan, and contact the owner or ISP hosting the IP address.
Refer to the following document on more information on how to block automated scanners from scanning your website
Here is the Apache documentation about access control (in case your web server is Apache)
If you are using IIS 8.0 and above, this document may help you to control access
If you are using IIS 7.0 and below, this document may help you to control access
If you are using another type of web server software, consult its documentation for information on access control.