Google has issued revised rules for Google Play apps in its continuing effort to stay one step ahead of nefarious developers. This time, the primary target is apps with pop-up ads that spoof a system, service or app notification and trick you into clicking where you shouldn't. It's also cracking down on "promotion or install tactics" that cause downloads or Play store redirects without your say-so, along with apps that send unsolicited SMS ads. Finally, it's forbidding any the use of "erotic content" to promote pornography and forcing advertisers to clarify when and how they use in-app purchases. Google will allow developers a 15-day grace period before it drops the ban hammer -- by which point the bad guys will have likely found workarounds.