What Is an ASN and Why It Matters for Fraud Detection
An ASN identifies the network that owns an IP range. Learn what ASNs are, how to look them up, and why they're one of the strongest signals in fraud detection.
ASNs are one of those behind-the-scenes internet concepts that turn out to be one of the most useful signals in fraud detection. If you only check one thing about an IP beyond its location, the network it belongs to is a strong candidate.
What an ASN is
An Autonomous System Number (ASN) identifies a network operator that controls a block of IP ranges and announces routes for them on the internet. ISPs, hosting providers, cloud platforms and big organisations each have one or more ASNs. Every public IP address belongs to exactly one ASN at a time.
In short: the ASN answers "who runs the network this IP lives on?"
Look up the ASN and owner of an IP
Why it matters for fraud
The type of network an IP belongs to is hugely predictive of risk:
- Consumer ISP ASN → likely an ordinary home or mobile user. Lower baseline risk.
- Hosting/cloud ASN → a server. End users rarely browse from servers, so a "customer" on a hosting ASN is suspicious — this is the core of datacenter proxy detection.
- Known-abusive ASN → some networks have outsized abuse; reputation reflects that.
This is why ASN context underpins VPN and proxy detection: most VPN exits and datacenter proxies live in hosting ASNs, and the mismatch between "claims to be a home user" and "lives in a datacenter" is one of the most reliable tells available. See how does VPN detection work.
How to use ASN data
- Look up the ASN for the IP via ASN data — you get the AS number and owning organisation.
- Classify it as residential, hosting/cloud, mobile or business.
- Feed it into risk. Combine the ASN type with anonymiser and reputation signals — or roll everything into one IP fraud score.
A note on nuance
ASN isn't destiny. Legitimate traffic comes from cloud ranges (corporate VPNs, API clients), and not every consumer ISP is clean. Use the ASN as one weighted signal among several, and allowlist known-good services rather than blanket-blocking a whole network.
Bottom line
An ASN identifies the network operator behind an IP, and that single fact — consumer ISP vs. hosting vs. abusive network — is one of the strongest signals in fraud detection. Look it up, classify it, and weight it alongside anonymiser and reputation signals.