Ulco from Netters.nl has written a post on bid management tool from Search Works leaks Adwords data. Ulco says that he accidentally discovered the possibility of viewing competitors CPC through a bid management tool which is used by large Dutch SEM firms. BidBuddy, an Adwords bid management tool which was created by The Search Works leaks the data through its cookies. It redirects users through the domain tsw0.com where it sets a cookie with the Adwords data.
Ulco further informs how to view such data:
The CPCs etc. can easily be discovered by using Firefox with the LiveHTTPHeaders plugin. If you open the LiveHTTPheaders screen before you click on one of the sponsored results you can literally just read the CPCs of your screen.