The web is good for this because there is so much that is unreliable.
Take this for example: http://zapatopi.net/treeoctopus/
The Pacific Northwest Tree Octopus? Really? I had students who were ready to believe this.
I also showed this one:
If you click the other tabs, you'll see the modified photo of a pregnant man. That usually gets them, even if they accept the notion of a rat with human intelligence.
If they still think the mouse and the man are legitimate, you can google the name of the supposed hospital, and you get articles about the author, including the following from The Daily Scotsman:
Yes, the whole thing – as you will know already if you followed the story at the time – is an elaborate “installation” by the artist Virgil Wong. According to the biography on Wong’s own website, www.virgilwong.com, he is head of web design and development for New York-Presbyterian Hospital and Weill Cornell Medical College, which would explain both his knowledge of medical jargon and the painstakingly professional sheen of the Dwayne Medical Center website. He is also an artist and film-maker whose various projects “all revolve around his interests in medicine, technology and the human body”.
I tried googling this in front of the students, where the students could see the computer screen projected. The results are not entirely clear. Consider, for example, the article in USA Today about this:
Dwayne Medical Center is listed first as a "hot site." Is it true? You can't really tell from this page. In fact, I'm not sure if the writers at USA Today realized it was a hoax.
Snopes.com is a good place to go from here - a website that helps you evaluate good (or bad) hoaxes and urban legends. There are some good examples of phishing scams there.
The focus, of course, is on developing strategies to verify and cross-check what you read on the Internet. It also segues nicely into persuasive writing and research.