• It is a program in which the malicious or harmful code is contained inside apparently harmless programing or data.
• Use to hack in a computer  by misleading users of its true intent
• Trojans can be employed by cyber-thieves and hackers by trying to have the opportunity access to users' systems.
•  Once it's activated, Trojans enable cyber-criminals to spy on users, steal sensitive and useful data, and gain backdoor access to user system.
• These actions can be include:
• Deleting data
• Blocking data
• Modifying data
• Copying data
• Disrupting the performance of computer networks
• Trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves ,unlike viruses and worms.

Here is the condition occur when Trojan comes to your computer :

• User tricked into loading and executing it on their system
• Popping up windows or changing desktop to damage the host by deleting files and stealing data.