[iframe src= url/ width=1 height=1 stye=visibility: hidden;][/iframe]
They have this configuration so that hackers can hide these unwanted iframes by making them invisible. The iframe is created with width and height of 1 pixel, visually it’s just a point. They also specify a style that makes it invisible: hidden;’
These iframes are invisible to web surfers but they can be detected in the HTML code of your web page.
Let us take the previous malicious iframe example and pack it. It would look like the following: