How IP blacklist and proxy detection actually works

When a website decides whether to trust your connection, it rarely asks who you are — it asks where your IP has been. Three signals dominate.

1. Who owns the address

Every IP belongs to an autonomous system (ASN). Addresses announced by hosting providers — AWS, Hetzner, OVH — are labeled datacenter; consumer ISP addresses are residential. Logging in from a datacenter range is exactly what bots do, so suspicion rises even when you are human.

2. What the address has done

Blacklist feeds aggregate abuse reports: spam waves, credential stuffing, scraper bursts. An address that once relayed spam can stay listed for months — and on shared hosting or VPN egress you inherit that reputation the moment you connect.

3. How many people share it

VPN servers and corporate proxies put thousands of users behind one exit IP. Some sites flag any shared egress; carrier-grade NAT (CGNAT) also triggers false positives for ordinary mobile users.

Why it matters

Shopping over an airport VPN, scraping your own site, or running a home server on a cloud VM can look identical to abuse. Checking an IP against ASN ownership, blacklists and proxy signals shows you how the internet sees it — before your bank does. Run an IP purity check and see all three signals in one report.