From the Arstechnica article:
Amero was substituting for a middle-school English class and asked the regular teacher permission to use the computer to e-mail her husband. The teacher granted her permission, and asked her not to log him out of the computer. Amero, the self-professed techno-noob, then left the room to use the restroom, and upon her return says that she found several students gathered around the machine looking at a web site. A series of unfortunate events occurred from this point on, resulting in a slew of pornographic pop-ups appearing on the screen. The onslaught continued despite Amero's attempts to close the windows.
According to The Register
When the students told their parents what had happened, they told the administration, who vowed that Julie would never work in the classroom again. But they went further. The 40-year-old substitute teacher was arrested, indicted, tried and here is the kicker on January 5, 2007, she was convicted of four counts of risk of injury to a minor, or impairing the morals of a child (Conn. Gen. Stat. 53-21). Indeed, she was originally charged with exposing 10 children in the seventh grade class to the materials on the internet, but six of the charges were dropped.
I guess "Ambush Porn" really is dangerous.