Mobile security vendor Lookout plans to start flagging as adware mobile apps that use aggressive ad networks if they don't obtain explicit consent from users before engaging in behavior that potentially invades privacy.Ad networks, advertisers and app developers have until June 24 to start conforming to the company's set of privacy and security best practices for mobile app advertising if they want to avoid being blacklisted."In 45 days, Lookout will classify as adware, ad networks that do not request explicit and unambiguous user consent for the following actions: display advertising outside of the normal in-app experience; harvesting unusual personally identifiable information; perform unexpected actions as a response to ad clicks," Jeremy Linden, security product manager at Lookout, said Friday in a blog post.According to a study released by Bitdefender in March, the number of adware apps for Android devices increased by 61 percent during a five-month period ending in January. In the U.S. in particular, the number of adware apps increased by 35 percent during the same period.Lookout, which is available for Android and iOS, expects apps to obtain user consent through stand-alone "easy-to-read modal alerts" if they want to deliver ads via the system's notification bar, place new icons and shortcuts on the mobile desktop, modify the browser bookmarks and homepage or modify the phone's ring tone.Apps must also ask users for explicit approval before collecting phone numbers, email addresses, browser, call and SMS histories or IMSI (International Mobile Subscriber Identity) numbers, Lookout said. In addition, in order to avoid being flagged as adware, apps must prompt for consent every time an ad click results in a phone call being initiated or an SMS message being sent."While the majority of mobile ads are legitimate, there are a few bad ad networks that put users at risk," Linden said. "Ad networks and advertisers are both the gatekeepers for vast amounts of personal data and an important part of the overall mobile ecosystem; it's important that they get user privacy right."According to Linden, during the past year, Lookout has observed a significant increase in the number of applications that use advertisements in a way that compromises users' privacy and interferes with their mobile experience.The company created its own Mobile App Advertising Guidelines in response to the lack of consistency across the mobile industry. "This lack of clarity gets in the way of tackling the problem," Linden said.Whether aggressive ad networks will actually adopt Lookout's best practices in order to avoid being flagged as adware remains to be seen. The company claims that its products are used by 30 million smartphone users.However, Lookout is not the only mobile security company that has noticed the increase in mobile adware and is taking a stance against it. Bitdefender, which offers a free antivirus product for Android devices, is also intercepting as adware those apps that use aggressive advertising and data collection practices."It's going to take a collective effort from both Google and mobile antivirus vendors to change privacy-invading practices, as intrusive adware will become even more widespread in the future," Liviu Arsene, security researcher at Bitdefender, said Monday via email. "While best practices for developers have also been issued by Google, a more hands-on approach would be interesting to see. Either by issuing 'trusted' certification for known and popular ad frameworks or by analyzing apps with more scrutiny from a privacy standpoint, the issue needs to be addressed."