Finfisher is a kind of computer software that can help people spy on other people's computers. It's kind of like a secret agent that sneaks into someone's computer without them knowing.
Now, why would someone want to use Finfisher? Well, some people might use it to spy on bad guys, like terrorists or criminals. But some other people might use it for not-so-good reasons, like to spy on their boyfriend or girlfriend, or their boss.
Finfisher can do a lot of things once it's inside someone's computer. It can look at their emails, read their text messages, and even see what websites they visit. It's not a good thing when someone uses Finfisher to spy on others without their permission, because it's like someone peeking through your window and watching everything you do.
So, always remember to keep your passwords safe, your computer protected with antivirus software, and to never download anything that you don't trust!