mnemonic offers passive DNS data to the public
mnemonic has set up a web interface for querying passive DNS [1] data collected in our malware lab. The data is classified as "TLP WHITE" [2], meaning that it may be shared freely.

https://passivedns.mnemonic.no/
mnemonic will also exchange passive DNS data with selected partners. These data are not available to the public, but will be available for our partners once suitable agreements have been made. As of July 1st 2014, the database contains in excess of 530 million entries, of which 60 million are "TLP WHITE".
We will be offering a JSON API available over HTTP. For an API description, please contact mss [a] mnemonic [dot] no.
Please note that we do not allow bulk querying. If you for some reason need access to bulk data, please contact mss [a] mnemonic [dot] no.
If you would like to exchange information or data, or need a place to publish passive DNS data, please contact mss [a] mnemonic [dot] no.
As the service is currently in beta, some unannounced downtime can be expected for service and upgrades.
[1] DNS name server responses are recorded, with a timestamp, in a database. This allows queries to uncover historical information for a host, domain or address, and searching for hosts and subdomains in a domain.
[2] https://www.first.org/tlp/