Wow, while talking with a couple of other Magento professionals today we uncovered an extension developer with a possibly nefarious scheme. One (or perhaps more) of their extensions adds a static page to your Magento installation which contains a large piece of advertising specifically about their development expertise. So far about 5000 Magento stores are affected.
The result, and affected shops, can be viewed by following the following URL with Google results: Google query affected shops. A couple of screenshots can be found below, showing the list of Google results and the static page which can be found when following the first result.
As always, beware of who you’re dealing with and what the extensions you are installing actually do in your store.