Viruses are the curse of computer operations! In these options, the hacker is the person trying to get into your private computing activities. The worm and the pirate are designed to foul up or even close down your computing activities.
The trojan horse is much more subtle and potentially deadly because it may be some time before you realise something is wrong. The scam is to get you to upload some useful app. - say "anti-virus" or 'clean-up" software free but the trojan horse is invisibly attached and can then carry out its evil work all the time you have that software, or even after you have deleted it. So Option A is correct.
A is the answer to this question. There are some people who are a bit unsure of how the Trojan is able to enter their computer. There may be some software that you can find online that will tell you that your computer’s ability to work will improve. Some may say that the performance can definitely be enhanced.
Since you do not realize that the software is disguised, you will download it. When this happens, you are allowing Trojan to enter your computer. Trojan does not automatically reveal itself. At times, you will not know that it is there until your hardware starts breaking down and you do not know what else to do anymore.