Code injection (often called cross-site-scripting or XSS ) is where a malicious user combines text and scripting to enter “malicious” values to your web page forms.
You have a system allowing users to register as members to your web site. Users are allowed to create their own username.
They fill out a form, and you save the data they set to the database.
Someone could create a user with the following username:
This allows attackers to add keyloggers, tracking scripts, or porn banners on your site, or just stop your site working altogether.
There is a similar problem if someone tries to enter smt. like this in the input field.
Mister XSS" onhover="some bad code
in the text field.
<input type="text" value="Mister XSS" onhover="some bad code" />