Frequently Asked Questions (FAQ)

For a complete list, see What does Censys scan?

We perform all IPv4 scans at least once a week and scan domains daily.

We provide academic and other non-commercial researchers with free access to Censys datasets on Google BigQuery as well as up-to-date raw scan data. This access is strictly limited to non-commercial use. [more information]

Censys scans help the scientific community accurately study the Internet. The data is sometimes used to detect security problems and to inform operators of vulnerable systems so that they can fixed. If you opt-out of the research, you might not receive these important security notifications. 

However, if you wish to opt-out, you can configure your firewall to drop traffic from the subnet we use for the measurements:

• 198.108.66.0/23

We do not remove results from Censys, but if you have blocked these subnets, the results will automatically be pruned out. 

While Censys often shows fewer hosts than Shodan, this is a difference in what results are displayed—not an artifact of Censys finding fewer in hosts. Censys only shows the current state of the Internet—we quickly prune out hosts that were not seen within the last week. In contrast, Shodan does not prune out old records. We are aggressive in pruning out old data because this allows users to accurately understand how the Internet is changing over time and prevent over counting due to DHCP churn and other IP changes. We've done in-depth of analysis of the devices found by both services in our research paper.

We provide geolocation data using the Maxmind GeoIP2 City Lite dataset.

Censys originally started as an academic research project at the University of Michigan. From 2015–2017, Censys was operated at Michigan with generous support from the Google Anti-Abuse Team. During this time, our license restricted access to non-commercial research. Since then, we've "spun-out" from the University of Michigan into an independent company. 

Censys was started by the same team that created ZMap, and Censys uses many of the ZMap tools to collect and annotate data. The ZMap Project is and will remain an independent open source project, but is primarily maintained by the Censys development team. 

We are staunch supporters of open source software and the Censys team plans to continue publishing new tools under the ZMap umbrella.

If you didn't find an answer to your question, feel free to reach to our team at support@censys.io.