Windows Remote Desktop Worm “Morto” Spreading

F-Secure Lab just found a new Internet worm, and it’s spreading in the wild. The worm is called Morto and it infects Windows workstations and servers. It uses a new spreading vector that we haven’t seen before: RDP (Remote Desktop Protocol). Windows has built-in support for this protocol via Windows Remote Desktop Connection
Once you enable a computer for remote use, you can use any other computer to access it.

When you connect to another computer with this tool, you can remotely use the computer, just like you’d use a local computer.

Once a machine gets infected, the Morto worm starts scanning the local network for machines that have Remote Desktop Connection enabled. This creates a lot of traffic for port 3389/TCP, which is the RDP port.
When Morto finds a Remote Desktop server, it tries logging in as Administrator and tries a series of passwords:
admin
password
server
test
user
pass
letmein
1234qwer
1q2w3e
1qaz2wsx
aaa
abc123
…….
………..
Once you are connected to a remote system, you can access the drives of that server via Windows shares such as \\tsclient\c and \\tsclient\d for drives C: and D:, respectively. Morto uses this feature to copy itself to the target machine. It does this by creating a temporary drive under letter A: and copying a file called a.dll to it.