The connection is that they all hide in the user's system and send information to the outside world, and they have certain rights to control the local machine on the remote machine.

The difference is that Trojan is a complete software, while the back door is small in size and single in function.

Moreover, in virus naming, backdoor is generally marked with the word "backdoor", while Trojan horse is generally marked with the word "Trojan".

Backdoor programs generally refer to those program methods that bypass security control and gain access to programs or systems. In the development stage of software, programmers often create backdoor programs in software to modify the defects in program design. However, if these backdoors are known by others, or the backdoor program is not deleted before the software is released, it becomes a security risk and is easily attacked by hackers as a vulnerability.

Backdoor programs, also known as Trojan horses, are used to lurk in computers and engage in information collection or hacker access. The biggest difference between backdoor programs and computer viruses is that backdoor programs may not copy themselves, that is, backdoor programs may not "infect" other computers.

The most famous backdoor program is Microsoft's Windows Update. The actions of Windows Update are nothing more than the following three: automatically connecting to Microsoft's website when starting up, reporting the current situation of the computer to the website for processing, and the website informs users whether there are files to be updated and how to update them through Windows Update program. If we analyze these actions, the action of "automatically connecting to Microsoft website when starting up" is the "latent" in the characteristics of backdoor programs, while the action of "reporting the current situation of the computer" is "collecting information". Therefore, although Microsoft "swears" that it will not collect personal computer information, if we analyze it from Windows Update, we will find that it must collect personal computer information before it can run. The only difference is what information it collects.