ICQ (from English I seek you) is a centralized instant messaging service of the Internet, currently owned by the investment fund Mail.ru Group. ICQ is a centralized instant messaging service that uses the OSCAR protocol. The service user works with the client program running on the device connected to the Internet. The messenger connects to the server. Through the server, a search and communication with other clients is carried out, and the exchange of service data, messages between users can be carried out either through the server or without its participation. As in most powerful network systems that serve a huge number of client requests, this server is not the only one and some of them are server clusters.

Service is commercial, but its use is free. Since its inception, the service belonged to its developer, Mirabilis, in 1998 it was sold to the American company AOL, and in April 2010 - to the Russian investment fund Digital Sky Technologies (DST). After the reorganization of DST in September 2010, ICQ became part of Mail.Ru Group.

Over the years, ICQ has released many customers and has undergone many changes. As of September 2013, the total monthly ICQ audience in Russia is 7.9 million (in the world - 12.3 million), at the end of 2014: in Russia - 6.7 million, in the world - 11 million.

IRC (English Internet Relay Chat) is an application layer protocol for real-time messaging. Designed mainly for group communication, it also allows you to communicate through private messages and exchange data, including files.

IRC uses the transport protocol TCP and cryptographic TLS (optional).

IRC began to gain special popularity after Operation Desert Storm (1991), when messages from all over the world gathered in one place and were broadcast on-line to IRC.

In view of the technical ease of implementation, the IRC protocol has recently become used in the organization of botnets as a means of transferring control commands to botnet computers from the owner.