The viruses, Trojans and system vulnerabilities you mentioned all refer to computer programs, and they are all named after the programs. Let me put it briefly: First of all, the system loopholes are actually caused by imperfect system program design. Program loopholes are inevitable and can only be fixed to an unlimited extent. Everyone should be able to understand this. Vulnerabilities are flaws in program design.
Computer viruses, which come from program codes, were not originally called viruses. However, because of their harmfulness and purpose, some computer professionals named them viruses. The earliest computer viruses were just because A small piece of program code produces phenomena and effects such as deadlock (infinite loop) due to writing defects. Some people use it for pranks, good-natured jokes, etc. Later, some people actually actively write and use the code maliciously to "wreak havoc" or "make profits" "So it became a virus. I won't talk about the specific characteristics of computer viruses.
Trojan horse is a type of virus. Simply put, it is a virus program that can reside in a poisoned computer, actively replicate, and actively "attack". Most Trojans attack computers mainly by copying and stealing in large quantities. Destructive attacks are extremely rare, but they cannot be ignored, because if the Trojan in the computer is often connected to the Internet or LAN, the Trojan program will, according to the coder's intention, Upgrade at any time and respond flexibly to computers. Although Trojans are good at hiding themselves, they are also easy to find. No matter what kind of virus, if you want to clean it, you must first remove the main program, process or server that resides in the memory from the memory, then remove its system attributes, and then "clear" it. I won’t go into details, the simple and easy-to-understand differences are the above.