A worm that replicates by sending complete, independent copies of itself over a network.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
Deloder is a network worm infecting Windows machines which have set a weak password to the Administrator account. It also installs remote access tool VNC, opening the computer to the world.
The worm scans random IP addresses, trying to locate Windows machines which have port 445 accessible. Port 445 (Microsoft SMB over TCP/IP) allows outsiders to access Windows file shares. This worm was found around noon GMT on Sunday 9th of March, 2003.
Most corporate machines are protected with centralized or distributed firewalls, which would block access to this port. However, many home computers have this port visible to the world and are vulnerable for this worm if the local administrator account has a weak password.
Once a suitable machine is found, the worm tries to log on to the remote computer using login name Administrator and by trying 50 different passwords:
If the login succeeds, the worm copies itself over (usually as INST.EXE) to several Startup folders and adds a key to registry to automatically execute DVLDR32.EXE (which is another copy of the worm).
When the machine is restarted, the worm starts to scan for new hosts to infect.
The main binary of the worm is packed with ASPack, once executed it drops psexec.exe and inst.exe.
The INST.EXE file drops several files into the system. A VNC server composed of the following files:
- psexec.exe (UPX packed, from sysinternals)
And an IRC backdoor, which will connect to servers from a list of 13, as:
- %windir%\Fonts\rundll32.exe (UPX packed)
Where %windir% is Windows root directory and %sysdir% is the WindowsSystem directory. The worm creates two keys in the Windows Registry, so that its components will be run next time Windows starts.
- [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run] Explorer = %windir%\Fonts\explorer.exe TaskMan = %windir%\Fonts\rundll32.exe
A side effect of the infection can be that shared folders might not be shared anymore.
F-Secure Anti-Virus detects this worm with the updates published on March 9th, 2003: