How did the police know that I had visited fraudulent websites?

Be blacklisted. This fraudulent website has been blacklisted by the National Anti-fraud Center. If you have the software of the National Anti-Fraud Center on your mobile phone at this time, the system will automatically push the IP that has logged into this website to the Anti-Fraud Center, and the police will know that they are browsing, and then the Anti-Fraud Center will distribute it to the police responsible for the address of each IP. They will be responsible for reminding in place, some will call to remind, and some will send text messages to remind.