"Can't I just use Shodan for this?" is a fair question. Both Shodan and Censys are excellent, widely respected tools, and security teams should know how to use them. The answer is that a search engine and a monitor are different instruments, the way Google is not an uptime checker.
What Shodan and Censys actually are
Shodan continuously scans the public internet and indexes what answers: open ports, service banners, device types, certificates. You query it like a search engine ("everything with port 9200 open in this ASN"), and it is the canonical tool for understanding internet-wide exposure. Censys does the same with a stronger emphasis on certificates and structured data, having grown out of academic internet-measurement work (the ZMap project). Both offer APIs and paid monitoring products aimed mainly at researchers and enterprise security teams.
Where the search-engine model falls short as monitoring
- Coverage is IP-first, not domain-first. Internet-wide scanners see hosts and ports. Your risk is organized around domains: DNS records, email authentication, security headers on named vhosts, certificate coverage for specific hostnames. Much of that is invisible to an IP-space crawl.
- Freshness is whenever the crawler last came by. Internet-wide scans revisit hosts on the crawler's schedule, not yours. A port that opened this morning may not be indexed for days.
- Nobody is watching for you. The data is there, but a human has to remember to query it, interpret raw banners, and diff against last time. That job silently stops happening after the second sprint.
- No remediation framing. A banner dump tells you what answered; it does not say which of it matters, what the severity is, or what change fixes it.
What a dedicated monitor does instead
Attack Surface Scan inverts the model. You register a domain, prove you own it with a DNS TXT record, and from then on the checks run on a schedule against that domain specifically: TLS and certificate health, HTTP security headers, SPF/DMARC/CAA, subdomain discovery from certificate transparency logs, lookalike-domain registrations, registration expiry, and TCP connect checks of common ports. Results are scored 0–100, every finding carries evidence and a fix, and (the part a search engine cannot do for you) changes generate alerts: critical ones immediately, the rest in a weekly digest.
Head to head
| Attack Surface Scan | Shodan / Censys | |
|---|---|---|
| Scope | Domains you have verified you own | The entire public internet |
| Model | Scheduled monitoring + change alerts | Query an index; monitoring products extra |
| Sees DNS, email auth, headers | Yes (core checks) | Partially (certs and banners, mainly) |
| Alerting on change | Built in, per domain | Available on paid tiers, IP/query-based |
| Audience | Teams responsible for specific domains | Researchers, threat intel, SOCs |
| Consent model | DNS ownership proof required | Scans everyone, by design |
Use both, differently
Keep a Shodan or Censys account: they are superb for one-off investigations ("what else is on this IP?", "is anything of ours in this vulnerable-device search?"), and their internet-wide view answers questions a domain monitor cannot. But make the recurring, boring, essential check (did anything about our domains change this week?) someone's automated job rather than an occasional manual search. That is what a monitor is for.
Frequently asked questions
Is Attack Surface Scan built on Shodan or Censys data?
No. Attack Surface Scan performs its own passive checks directly against domains their owners have verified: HTTP requests, TLS handshakes, public DNS queries, certificate transparency log lookups and TCP connect checks. It does not scan the wider internet and does not index third-party hosts.
Can Shodan alerts replace an attack surface monitor?
Shodan's paid monitoring can alert on changes for IPs and search queries, and for port-exposure tracking it is genuinely useful. It does not, however, evaluate DNS records, email authentication (SPF/DMARC), HTTP security headers, certificate expiry timelines or lookalike domains; most of a small organization's real drift happens in exactly those layers.
Is it legal to look up my company on Shodan or Censys?
Yes: querying an existing index is not scanning. Both services scanned the internet themselves and publish what answered. Using them to research your own footprint is a standard, legitimate security practice.