I've had a few people ask me about weird spammy downloads on their Android devices. They download a free app, and then the next day they've got two or three new apps appearing on their Home screen. Things like poker games they didn't download or links to a "market" that doesn't appear to be part of the Google Play store. What gives?
What they've accidentally downloaded is an app that uses icon spam. It's one of a couple of particularly annoying ad spam techniques on Android. Here's more on that and how you can avoid it.