Joshua Porter has written an article on the how recommendation systems are changing the Web. He lists several benefits and drawbacks stemming from these technologies. It is cool to observe that our group is actively researching to improve three of the four "drawbacks" that he lists:

• Dan Frankowski is working on Recommenders Everywhere - one attempt to make recommendation systems easier to set up
• Dan Cosley is working to providing tools that help communities build and maintain good databases
• Tony Lam is working to understand shilling in recommender systems
  

Seth Godin has a blog about the end of digg/reddit.  He creates a cute analogy to the "pencil drop", where the students in a class will all agree to drop their pencil at the same time to annoy the teacher.  He argues that this sort of effect will lead to shilling on social news sites, where a group of people will all agree to take action at the same time to get a chosen article seen.

One possible counter to this phenomenon is the personalized social news site, where each user sees the news he or she wishes.  On this site the shill has less to gain, because he can influence only those people who agree with his past decisions, and shills will have limited effects, because people's profiles will learn to ignore them.  (On the other hand, personalized shills may still be a problem, but that's another story.)

Social news sites are becoming hot-beds of shilling. Shilling is the act of pretending to like something, in order to convince someone else to take an action. (There's a fun discussion on the talk page of the Wikipedia article named "Shill" about exactly what activity should be classed as shilling, and what activity is just lying. I tend to take an inclusive view on the subject: if you're lying to try to make someone think something is better, you're shilling.)

Niall Kennedy has a lovely blog entry about how he was able to track down the back-story on a couple of shilling attacks on the news aggreggation site digg. His article contributes two particularly fun parts of the story:

Amazon reviews and tags don't always get used "seriously" -- the Kevin Federline album Dan linked to is a great example. It's been somewhat of a Amazon tradition to target certain products with irreverent and funny reviews. Sometimes, they're removed by Amazon since they're pretty inappropriate, but others, such as reviews for David Hasselhoff's album, whole milk, or recreational tanks (...interesting cross-sells!) have been left alone.

Now, the point of writing these reviews is probably not to shill for the products and make more sales, but their existence has undoubtedly driven disproportionate amounts of traffic to the product pages since people find them funny and send the links to their friends. How does phenomena like this fit in with recommender system security? Is Amazon benefiting from it?