Trojan is malware that is usually downloaded, mistaking it for legal. The name refers to the semi-mythical story of the Trojan horse, with which the Greeks captured Troy in the 13th century BC (sometimes the Trojan is called the “Trojan”, which is incorrect, since the Trojans just happened to be affected.).
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A Trojan differs from viruses and worms in that it does not reproduce. It takes root in a computer, smartphone, tablet to work unnoticed by the user. For example, it transfers personal information to a third party — bank card data, electronic documents, usernames, passwords. There are also proxy Trojans that use an infected device to send spam; spyware Trojans that can read correspondence in messengers; backdoor Trojans that provide access with administrator rights (for the latter, see a separate article). In addition, Trojans are used as “pads” to anonymize hackers: unauthorized access to the banking network can be performed not from the attacker’s IP, but from the IP of an infected machine.
The Trojan is often downloaded along with “cracked” software from torrent aggregators. At the same time, to install software without a license, you need to use a “keygen” (key generator) or a “crack” (cracker). Trojans are disguised under them.
Another popular source is emails with attachments like an image or other media file with an intriguing name. The option is more designed for completely inexperienced users.
In addition, Trojans are found on fake sites — for example, those that mimic the official sites of mobile operators. This was the case with Skygofree Android Trojan, discovered in 2018. After downloading, the Trojan gained full control over the smartphone, including over the messengers Skype, Viber, Facebook Messenger and WhatsApp.