The Electronic Frontier Foundation (EFF) has published an extensive study into the hidden techniques and methods used by online service providers to collect and track our personal information and activities. On Monday, as shoppers plundered e-commerce websites for Cyber Monday bargains, the civil and privacy rights outfit released "Behind the One-Way Mirror," outlining corporate surveillance methods with a focus on behind-the-scenes tracking. The paper covers a variety of different tracking methods including browser fingerprinting, invisible pixel images, social widgets, mobile tracking, and facial recognition employed by tech giants including Amazon, Facebook, Google, Twitter, as well as countless data brokers, to "collect information about who we are, what we like, where we go, and who our friends are." Third-party tracking is usually invisible to the naked eye. Code, images, and plugins can all contain functions that track browsing, activities, purchases, the duration of visits, ad engagement, and clicks, and may link up different data sources to create a comprehensive shadow profile of your digital self. According to the EFF, for example, Facebook uses invisible "conversion pixels" to collect data on third-party websites and to track ad engagement; Google uses location information to track user visits to physical stores and makes use of transparent pixel images for tracking, and smart home devices -- including Amazon Echo and Google Home -- can harvest audio data and may be used by human employees to improve voice recognition technologies.