Rumor source detection approaches are broadly divided into two main categories: 1) single source detection approach and 2) multiple sources detection approach [10]. Single source detection approaches are query-based, anti-rumor-based, network observation, etc. Multiple source detection approaches are network partitioning, ranking-based, community-based, approximation-based, etc. Single source detection using network observation again has three types of observations such as snapshot, complete and monitor observations, etc. Query-based observation allows to find source of rumor by asking queries to neighbors about rumors [18], anti-rumor-based is by diffusing anti-rumors into the network can get information about network using monitor-based observation and use this information to find rumor source [19]. Multiple sources of rumor is also a challenging task, and can be done by network partitioning using rumor centrality metric [20], community-based which follows SIR model and reverse diffusion [21]. All these models are useful to find rumor source in online social networks. Rumor source identification and punishing the culprit reduces further diffusion of rumors and cyber-crimes in social networks. This survey explains in the rest of the chapter social networks and their features in Section 1.2. What is cyber-crime, various cyber-crimes and their impacts, cyber-crimes in social networks are discussed in Section 1.3. Rumor detection using classification models in Section 1.4. Factors consider in rumor source identification and its classifications are discussed in Section 1.5. Rumor source detection categories such as single source and multiple sources of rumor in network are discussed in Section 1.6. Summary of this survey is discussed in Section 1.7.
1.2 Social Networks
A social network is a website that allows people to make social interactions and personal relationship through sharing information like photos, videos, messages and comments, etc. [22].
1.2.1 Types of Social Networks
There are many social networking sites, among these some sites like Facebook, WhatsApp, Twitter and Instagram that have become popular platforms over a short period for social interaction across the world [3]. But the options available in these networking sites are limited even though they are popular. There are other social networks, which are having more number of options but not popular. All these social networks are classified based on the options like sharing photos, videos, thoughts of personal or professional which are available for people to interact and collaborate each other. The following categories explain about how each one classified based on available options. Figure 1.1 depicts various social networks available online.
Figure 1.1 Social networks [23].
The major benefit of social networks is keeping in touch with family members and friends. The following list shows the most widely used social networks for building social connections online. Table 1.1 shows users for each network in millions.
Table 1.1 Social network users [24].
| Service | Active users (in millions) |
| 2,320 | |
| YouTube | 1,900 |
| 1,600 | |
| Facebook Messenger | 1,300 |
| 1,098 | |
| 1,000 | |
| 807 | |
| Qzone | 532 |
| TikTok | 500 |
| Sina Wiebo | 462 |
| 330 | |
| 330 | |
| Douban | 320 |
| 303 | |
| Biadu Tieba | 300 |
| Skype | 300 |
| Snapchat | 287 |
| Viber | 260 |
| 250 | |
| Discord | 250 |
| LINE | 203 |
| Telegram | 200 |
Facebook: Facebook is arguably the most popular social media service, providing users with a way to build relationships and share information with people and organizations that they choose to communicate with online [3].
WhatsApp: It is a real-time social network that arrived later than Facebook but has evolved in a short time by offering user-friendly features such as quick messaging, sharing photos, videos, documents, voice and video calling, group chatting and protection for all these, etc. [3].
Twitter: Share your thoughts and keep ahead of others through this platform of real-time information [3].
YouTube: YouTube is the world’s largest social networking site for video sharing which allows users to upload and share videos, view them, comment on them, and like them. This social network is available throughout the world and even enables users to create a YouTube channel where they can share all of their personal videos to show their friends and followers [3].
Google +: The relatively new entrant to the social interaction marketplace is designed to allow users to establish communication circles with which they can communicate and which are integrated with other Google products [3].
MySpace: Though it initially began as a general social media site, MySpace has evolved to focus on social entertainment, providing a venue for social connections related to movies, music games and more [3].
Snapchat: