SilverPush’s company policy is to not « divulge the names of the apps the technology is embedded, » meaning that users have no knowledge of which apps are using this technology and no way to opt-out of this practice. As of April of 2015, SilverPush’s software is used by 67 apps and the company monitors 18 million smartphones.
SilverPush’s ultrasonic cross-device tracking was publicly reported as long ago as July 2014. More recently, the company received a new round of publicity when it obtained $1.25 million in venture capital. The CDT letter appears to be the first time the privacy-invading potential of the company’s product has been discussed in detail. SilverPush officials didn’t respond to e-mail seeking comment for this article.
Source : Beware of ads that use inaudible sound to link your phone, TV, tablet, and PC | Ars Technica