The worm is loaded automatically by changing the following keys in the
registry.
HKEY_CLASSES_ROOT\exefile\shell\open\command
if you have deleted the worm before fixing the registry your applications
won't work.
You can check the system manually. I-Worm/Yaha creates
the file "MSMDM.EXE" in Recycled folder. The presence of this file ensures
you are infected with this worm.
Yaha Worm changes registry keys when infecting the
machine and it should be fixed before deleting the main worm file
"MSMDM.EXE" stored in Recycled folder
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Check out the Symantec site on this Yaha virus. If it has run it will stop
all .exe file open actions. There are step by step instructions how to go
into the safe mode dos command and change regedit
From the Symantec site
If the worm has run, do the following:
1. Download the updated virus definitions using the Intelligent Updater, but
do not install them.
2. Restart the computer in Safe mode.
3. Copy Regedit.exe to Reg.com.
4. Edit the registry and reverse the changes the worm made.
5. Start your Symantec antivirus software. If it does not start or properly
function, re-install it.
6. Install the Intelligent Updater virus definitions you downloaded earlier
(step 1).
Copying Regedit.exe to Reg.com
Because the worm modified the registry so that you cannot run the .exe
files, first make a copy of the Registry Editor as a file with the .com
extension, and then run that file.
Windows 95/98 users: Click Start, point to Programs, and click the MS-DOS
Prompt. (This opens a DOS window at the C:\Windows prompt.)
2. Type the following, and then press Enter:
copy regedit.exe reg.com
3. Type the following, and then press Enter:
start reg.com
1. Navigate to and select the following key:
HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command
CAUTION: The HKEY_LOCAL_MACHINE\Software\Classes key contains many subkey
entries that refer to other file extensions. One of these file extensions is
.exe. Changing this extension can prevent any files ending with an .exe
extension from running. Make sure that you browse all the way along this
path until you reach the \command subkey.
Modify the HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command
subkey, :Modify this(command) key.
2. In the right pane, double-click the (Default) value.
3. Delete the current value data, and then type: "%1" %* (That is, type the
following characters: quote-percent-one-quote-space-percent-asterisk.)
When you click OK, the (Default) value should look exactly like this:
""%1" %*"
Make sure that you completely delete all the value data in the command key
before you type the correct data. If you leave a space at the beginning of
the entry, any attempt to run the program files will result in the error
message, "Windows cannot find .exe." If this happens to you, start over at
the beginning of this document, and make sure that you completely remove the
current value data.
4. Navigate in turn to each of the following keys:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\
CurrentVersion\RunServices
NOTE: The RunServices key may not exist on all the systems.
5. In the right pane, delete the value
WinServices C:\%System%\WinServices.exe
6. Exit the registry editor.
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source of scripts that will do the above repair
http://home.earthlink.net/~rmbox/Reticulated/Only_IE.html
exefix8.com is described as doing the best repair to the registry .exe open
command