Whenever you clicked on an unknown file or download or open something from unknown link, the same time malware take entry in our system.
When you execute the program, the malware can spread to other files and damage your computer.
Backdoor trojan is type of malware, Trojan can create a “backdoor” on your computer. It lets an attacker access your computer and control it. Your data can be downloaded by a third party and stolen. Or more malware can be uploaded to your device.
Malware named RAT
A remote access Trojan (RAT) is a malware program that includes a back door for administrative control over the target computer.
RATs are usually downloaded invisibly with a user-requested program such as a game or sent as an email attachment. (ex. Ads while surfing internet)
Once the host system is compromised, the intruder may use it to distribute RATs to other vulnerable computers and establish a botnet.