Okay, Monrovia's Library page (this one: http://www.ci.monrovia.ca.us/monrovia-public-library ) has indeed been hacked and is being used to sell Viagra.
If you click on the link in the previous paragraph you will see nothing about Viagra, but if you pretend to be the Google crawler coming by to check if anything is new, then you see all the Viagra stuff you see above and more, and the links to Viagra websites you see in the bottom image.
Non-techies can skip this. Here's how I got the page. On a Linux system command line I used wget http://www.ci.monrovia.ca.us/monrovia-public-library --user-agent="googlebot" to output the page as Google sees it to my desktop, then renamed it to have a ".html" extension, then viewed it with my browser.
So, what is the point of creating a page with links to Viagra websites if it cannot be seen by actual people who might buy the stuff? Well, my guess is that because one way Google ranks pages is by how many reputable websites link to the page, therefore, whenever Google drops by to see about the Monrovia Library, it finds that site is linking to Viagra sites, so it bumps up in its the listings those particular Viagra sites that are linked to by the City of Monrovia, among others.
- Brad Haugaard