This machine is running a continuous Internet scan, mapping changes in the Internet over time. We are doing our best to make sure that it has only a light impact on your network, but if you feel that it's causing a problem (or just don't like us), we'll happily add you to our "exclude-file" to remove your from the scan. If you have questions, concerns, or want to opt out please contact us at email@example.com
If you'd like to chat abut this in public, you can use my Twitter handle @ErrataRob.
As of October, 2013, we are currently scanning ports for commonly used services including HTTP, SMTP, SSH, SNMP, etc.... It does not try to log in. For instance with HTTP: The probe waits for a few seconds for a banner, and if no banner is received, sends an HTTP "HEAD" query. Also searches for popular malware like Zeroaccess tojan and vulnerabilities like the Dlink auth bypass have been added.
Source code for our scanner is available at https://github.com/robertdavidgraham/masscan. It's a useful tool if you want to do large surveys of your own internal network.