What has Blake just accomplished?

Blake is in charge of securing all 20 of his company’s servers. He has enabled hardware and software firewalls, hardened the operating systems, and disabled all unnecessary services on all the servers. Unfortunately, there is proprietary AS400 emulation software that must run on one of the servers that requires the telnet service to function properly. Blake is especially concerned about this since telnet can be a very large security risk in an organization. Blake is concerned about how this particular server might look to an outside attacker so he decides to perform some footprinting, scanning, and penetration tests on the server. Blake telnets into the server using Port 80 and types in the following command:

HEAD / HTTP/1.0

After pressing enter twice, Blake gets the following results:

What has Blake just accomplished?

A.
Downloaded a file to his local computer

B.
Submitted a remote command to crash the server

C.
Poisoned the local DNS cache of the server

D.
Grabbed the Operating System banner

Explanation:
In the context of Computer Networking, Banner Grabbing is an enumeration technique used to glean information about computer systems on a network and the services running its open ports. Administrators can use this to take inventory of the systems and services on their network. An intruder however can use banner grabbing in order to find network hosts that are running versions of applications and operating systems with known exploits.