ICQ is an instant messaging client, which was first developed and popularized by Israel company mirabilis in 1996. The name of ICQ comes from the English phrase "I seek you". Ownership of ICQ was transferred from mirabilis to AOL in 1998 and AOL to AOL in 2010 Mail.Ru Group.

ICQ client applications and services were originally released in November 1996 and can be downloaded for free. Users can sign up for an account and be assigned a number, such as a phone number, so that others can contact them (users can also provide a handle). ICQ is the first independent instant messaging program and one of the first online instant messaging program services, while real-time chat itself is not a new function of the Internet (IRC was the most common platform at that time). It is a concept of fully centralized service. Personal user accounts focus on one-to-one dialogue, and set a blueprint for later instant messaging services (such as aim). Its impact is now Visible in social media applications. Although Internet Relay Chat programs such as arch and MIRC occupy a dominant position in the market, their popularity begins to decline with the emergence of mobile computing, which has begun to occupy a place in PalmPilot and the emerging Microsoft Windows compact edition.

ICQ peaked around 2001, registering more than 100 million accounts. Acquired in 2010 Mail.Ru About 42 million users a day. Since 2013, ICQ has 11 million users per month.

ICQ users are identified and distinguished by sequentially assigned uins or user identification numbers. The UIN was invented by mirabilis as the user name assigned to each user during registration. The issued UIN starts with "10000" (5-digit number), and each user will receive a UIN when registering with ICQ for the first time. Starting with ICQ6, users can also log in using the specific email address associated with their UIN during the initial registration process. Unlike other instant messaging software or web applications, on ICQ, the only permanent user information is UIN, although you can search for other users using their associated email address or any other details that are exposed by updating the information in the account of the account. Disclosure of personal data. In addition, users can change all their personal information, including screen names and email addresses, without having to re register. Since 2000, ICQ and aim users have been able to add each other to their contact lists without any external clients. In response to the theft or sale of an attractive UIN, ICQ began to store email addresses previously associated with the UIN. [5] In this way, stolen uins can sometimes be recovered. This only applies if (since 1999) a valid primary email address is entered into the user's profile.