Tbh the advice provided is already pretty accurate, as to how; there’s a non zero chance that a friend may have sent you a RAT (remote admin tool/remote access Trojan), these are basically the best back door to someone’s computer you can have, normally you want to have physical access to someone’s computer to install them or have a user run it with elevated privileges, (there are other ways as well, such as spoofing a jpg, other methods of remote code execution). These tools will allow you to access there computer, files, keylog, steal passwords, send popups, open and close the disk tray plus basically anything else you could do with access to the computer.
Basically follow other people’s advice in regards to undoing this.
Unrelated beyond the Tories being retarded with banning things for no real reason: I’ve just discovered that they’ve effectively banned the sale of sodium hydroxide (drain cleaner) and potassium hydroxide (used to make soap), before I could buy them on eBay or get the sodium hydroxide at any super market, but now I have to go via a chemical supply company, taking literal weeks, and paying £7 for 100g of sodium hydroxide, where I used to be able to get 500g for £2.
They’re scum for an endless list of things but this has really annoyed me.