Hackers use cross-site scripting, also known as XSS, to gain control of the content of your web pages. They do this by entering a piece of malicious code into your site, usually through an existing input field, such as a search box, or name/address box. If your website is not set up to fight off this sort of invasion, the hacker will be able to take control of your site, even gathering personal information from your trusting customers.
The SiteLock Deep 360-Degree Site Scan will test each and every one of the input fields on your site by inserting code into them, just as hackers would (but SiteLock's code is harmless!).
To avoid an XSS attack, make sure all your applications and scripts are up to date and, where possible, reduce your risk of third-party plugins. If the SiteLock scan finds a vulnerability, you'll need to quickly verify and harden your code for security.