## 2 Theoretical Background  
_An Overview of Commonly Used Services and Collected Data from Users_  
Nowadays, users of various Internet platforms exchange different types of data, including their personal information, such as name, age, gender, location, etc., in order to use their preferred services. Some of the users are aware of the potential risks associated with privacy breaches, but there are also users who are not concerned when sharing their data or are even aware of the possible consequences of data leaks. For example, Google collects various types of data that help the company to personalize and target advertising to users, especially data linked to the user's identifier. Google may also use some data to monitor the continued functionality of its applications. This may include diagnostic and crash data that inform the company or organization on why a particular application stops working on certain user devices at different times. On the other hand, when capturing user activity, such as a shopping session, a user may use Google to search for a book, then visit the Wikipedia page to learn more about it, compare prices on Amazon, and then complete the purchase on the website. Later, the same user might start experimenting with technology after seeing a post about the latest iPad model on a friend's Facebook page. This sequence of an individual's online activities comprises visits to various websites across different categories, reflecting a combination of the user's various interests and behaviors [3]. In this survey paper, we have analyzed some of the most widespread Internet services aimed to see how many users use them. We selected some Google services and some other services, based on their popularity and from usage statistics presented in the paper [4]. According to statistics, Google and its services dominate the global search market, holding a significant majority share. These statistics highlight their significant impact, which is why we mostly focused on them. Besides the most common parameters, we have also introduced accessibility parameters because this is something specific that recent privacy regulations have brought to our attention as a new factor. These parameters are becoming more relevant due to their importance for meeting the needs of people with various disabilities, even though it is not yet so widespread. In this sense, we will describe some of the most popular Google services and the data collected by each service for personalization purposes. The commonly used Google services that we focus on include YouTube, Gmail, Google Search, Google Assistant, Google Play Store, Google Maps, and Google Calendar. On the other hand, we also examine other popular Internet services to compare the data they collect with that of Google services and to identify similarities in their data collection and processing practices. Google uses several methods to collect user data. The most obvious are the explicit ones, where the user actively and knowingly provides information to Google, e.g., when logging in to one of the popular services, such as YouTube, Gmail, Search, etc. Implicit methods are less obvious ways for Google to collect user data, where an application collects information while it is being used, possibly without the user's understanding. Google's passive data collection methods arise through platforms (e.g., Android and Google Chrome) and applications (e.g., Google Search, YouTube, Google Maps, Google Analytics, AdSense, Ad Mob, AdWords, etc.) [5]. In general, Google uses a wide range of parameters in its various services to provide personalized experiences to its users. For example, Google Search uses various parameters to personalize search results, including search history, location, language, device type, etc.