If I am taking data from a website, for example status updates from Facebook and showing them on my website. What possible damage can be caused if I am not taking into account that the code written as status update would execute on my website?
For example, Mr. Simon has putted his status update,
"<p style="color:red;">I love to code</p>"
Now, when I display this on my website, it transforms into the text I love to code written in red.