Fake tech support or "authority". Bad behavior may include fake computer error messages or warnings; fake branding that imitates trusted companies (phishing) such as Amazon, Google, or Microsoft, or pretense that such companies are clients; fake trust seals; and fraudulent payment methods.
Risks: tracking, spam, credit card fraud, identity theft, malware.
Do not call, answer, or follow instructions from these people. Do not allow them to access your computer. Do not provide any financial or personal data.