Here's how Happy99.exe infects your system:
It will create two files in the Windows System folder, SKA.EXE and SKA.DLL. SKA.EXE will be a copy of HAPPY99.EXE. It will copy the original WSOCK32.DLL to WSOCK32.SKA. Then it will modify WSOCK32.DLL without changing its size so it will try to run SKA.DLL while posting to Usenet and sending E-Mail. The SKA.DLL file will silently attach HAPPY99.EXE to a second copy of outgoing newsgroup and e-mail messages with a barely noticable delay.
It does not modify any other file besides WSOCK32.DLL. WSOCK32.DLL is a regular part of Windows that provides a connnection to the Internet. If it is unable to modify WSOCK32.DLL, then it will add SKA.EXE to the RunOnce section of the registry and WSOCK32.DLL will be modified next time the computer starts. It will still create WSOCK32.SKA even if it is unable to modify WSOCK32.DLL. This virus will keep a list of message recipients in the file LISTE.SKA in the Windows System folder. It will try not to send the Happy99.exe file twice to the same person.
Since it gets passed along a lot, a different virus could attach to HAPPY99.EXE somewhere along the way. Without SKA.DLL and SKA.EXE, the modified WSOCK32.DLL cannot perform any viral action. However using a modified WSOCK32.DLL could cause problems while on the Internet. The most common problem that has been reported is invalid page faults, but these can have other causes. Restoring the original WSOCK32.DLL will correct these problems.
This virus does not affect Macs, DOS, Windows 3.x, OS/2, Linux or WebTV. However, someone using one of those could pass it along manually, for example by forwarding the message. Under Windows NT it will create SKA.EXE, SKA.DLL, and WSOCK32.SKA but will fail to add itself to the registry or modify WSOCK32.DLL. If you have NT, you don't have to follow the removal steps; you can simply delete SKA.DLL and SKA.EXE from inside Windows NT if you would like.
Some people have asked whether it is always called HAPPY99.EXE. This virus doesn't contain any code to change the name. However, it would be simple for a person to change it to anything they like.
It contains the encrypted text:
"Is it a virus, a worm, a trojan? MOUT-MOUT Hybrid (c) Spanska 1999."
Download the following file, unzip it and run it in Windows95 or Windows 98 by double-clicking on it. This small program will perform the steps seen in the manual removal method with no user intervention. Once the program is run, your system will want to reboot. This must happen to completely remove the happy99.exe worm.
Craig Schmugar's Happy99Cleaner program (click to download)
Manual Removal of Happy99.exe
Steps marked optional are not absolutely necessary and are completely safe to skip. If you're not comfortable with DOS, get someone knowledgable to help you with this. I cannot make guarantees of perfect safety since its a manual removal, Perform these at your own risk. If you have Windows NT, you don't have to follow the removal steps.
1. Click Start, then Shut Down, then "Restart Computer in MS-DOS mode", then click Yes. It's important to exit Windows in order to be able to replace the file WSOCK32.DLL which Windows normally has in use.
2.At the DOS prompt type this exactly and press enter at the end of each line:
3. Delete SKA.EXE and SKA.DLL by typing
If you get "File not found" you're either not infected or in the wrong directory. Make sure you're in your Windows System directory; check to see if you followed step 2 exactly.
4.Copy WSOCK32.SKA to WSOCK32.DLL by typing
ATTRIB -R WSOCK32.DLL
COPY WSOCK32.SKA WSOCK32.DLL
Answer "Yes" if it asks if you want to overwrite WSOCK32.DLL.
WSOCK32.SKA is a backup of the original WSOCK32.DLL. You are replacing the modified DLL with the original. If you get a "Sharing violation" make sure you followed step 1.
5.Optional Delete WSOCK32.SKA by typing
You can leave WSOCK32.SKA on your system. It is a copy of your original WSOCK32.DLL Do not delete WSOCK32.SKA if you are unable to replace WSOCK32.DLL with WSOCK32.SKA.
6.Return to Windows by typing
7.Optional Delete Windows Registry Key.
Click Start, then Run, then type regedit in the text box, then click OK. Click HKEY_LOCAL_MACHINE, then Software, then Microsoft, then Windows, then CurrentVersion. Under RunOnce check for SKA.EXE and select it if it is there. Press delete and then click Yes. Close Regedit. Don't change anything else without making a backup of the registry first. If you don't find SKA.EXE in the registry, it doesn't mean you're not infected. SKA.EXE is only added to the registry if HAPPY99.EXE is unable to modify WSOCK32.DLL when you run it. Also, you'll only find it in the registry if you haven't rebooted since you ran HAPPY99.EXE.
8.Optional Choose Start, Programs, Accessories, Notepad, choose File, then Open then type C:\WINDOWS\SYSTEM\LISTE.SKA in the File Name box. Warn the people on the list, then delete LISTE.SKA. Make it clear to the people you warn that they won't be infected unless they ran happy99.exe, to avoid alarming them unnecessarily. If you haven't sent out any infected e-mails, there won't be a LISTE.SKA.
9. Optional Delete the HAPPY99.EXE file. The location of HAPPY99.EXE will vary depending on where you saved it. You can delete it simply by dragging it to the Recycle Bin from within Windows or whatever method you prefer. You may still have some messages with HAPPY99.EXE attached in your mailbox. These cannot do anything unless you run them. You can delete them if you want to or just ignore them. 10.Optional If you aren't sure whether WSOCK32.DLL is infected, choose Start, then Find, then "Files or Folders". Then type WSOCK32.DLL in the "Named" box. In the "Look in" box choose drive C: or whatever drive you have Windows on. In the "Containing Text" box type "ska.dll" without the quotes. Then click "Find Now". If you don't find any files, that means that wsock32.dll isn't the modified version. If you don't have the modified WSOCK32.DLL, the virus has no way to attach to e-mails, even if you have SKA.EXE, SKA.DLL, and WSOCK32.SKA in the Windows System folder. If you have SKA.EXE in the RunOnce registry section, and you haven't deleted SKA.EXE, then the virus will try to modify WSOCK32.DLL the next time you restart the computer.
Make sure you type the instructions exactly including spaces and punctuation. You might want to print out the removal instructions so you have something to refer to. If you're having trouble with the DOS commands, get a local person to help you with them. It's hard to know exactly how you're typing the DOS commands and what your exact situation is without seeing it in person.Source: http://www.pchell.com/internet/happy99.shtml