1) Through ISPs: Internet Service Providers (ISPs) can track the online activities of their customers. If an ISP suspects that a customer is illegally downloading music, they may send them a warning letter. If the customer continues to download music illegally, the ISP may terminate their service.
2) Copyright trolls: Copyright trolls are companies that buy the rights to copyrighted material and then sue people who illegally download it. Copyright trolls often use automated software to track down people who are illegally downloading music. If they find someone who is illegally downloading music, they will send them a demand letter. The demand letter will usually state that the person has to pay a certain amount of money to settle the case, or they will be taken to court.
3) Government agencies: Government agencies can also investigate and prosecute people who illegally download music. The FBI, for example, has a dedicated unit that investigates online copyright infringement. If the FBI catches someone illegally downloading music, they may be charged with a crime.