I think the title explains the situation quite precisely. When I try to run it in cmd it gives me a message box saying:

"c:\WINDOWS\system32\cmd.exe - ping
The NTVDM CPU has encountered an illegal instruction.
CS:0577 IP:0102 OP:0F 04 30 3c 39 Choose 'Close' the terminate application."

-I press ignore-

"c:\WINDOWS\system32\cmd.exe - ping
The NTVDM CPU has encountered an illegal instruction.
CS:0156 IP: 04df OP:0f a7 00 22 00 Choose 'Close' the terminate application."

-ignore again-

"c:\WINDOWS\system32\cmd.exe - ping
The NTVDM CPU has encountered an illegal instruction.
CS:1056 IP:051f OP:63 3a 5c 77 69 Choose 'Close' the terminate application."

And then the program closes.

If I try it in Command.com then it spews forth lines of random characters and then crashes. I mean the DOS command prompt crashes, not just the ping. The ping doesn't even open.

I have had this for an indefinite amount of time, but long enough so that system restore can't fix it, and I'm not sure if it's even fixable. Would anybody be willing to post their non-corrupt ping command?

Do the following:
Start - Run
cmd
ping.exe (don't forget to type out the extension .exe !)

if that works you probably have a virus named ping.com.
Get rid of it and everything should be back to normal.

As for ping.exe just google it.

Okay, I entered

Ping.exe YouTube.com

and it worked... I guess I have the ping.com virus? Should I fix it or just keep entering ping.exe from now on?

Looks to me like something else on your path is named ping, and it's catching you ping call before windows finds ping.exe.

Search your system for files called ping, and try running different ones from the command prompt. If you find one that returns the error you originally posted about, try deleting it.

I'd never leave malware on my computer, especially if I already identified it. So yes, do a search for ping.* and scan all found files for viruses.

If your virus scanner doesn't detect a virus in any of these files I'd suggest renaming all pings that have executable extensions to something non-executable.
For example when "ping.com" is found rename it to "ping._com".

Seems kind of a dumb way to make malware, though. Be better to make an infected version of ping that actually did execute properly and give you expected results, while also doing malware-ish type things in the background. If they had done that, then in this case c(O.Oc) would have been none-the-wiser that something nefarious may have been going on.

You need this. http://www.technize.com/?dl_id=67

Well, I have just concluded my search for ping.* and I found six files! They're all in weird places too! allow me to elaborate with a table.

#) file name folder
1) ping C:\i386
2) ping C:\WINDOWS\$NtServicePackUninstall$
3) PING.EXE-03254B67.pf C:\WINDOWS\Prefetch
4) PING.EXE-30F9CA9D.pf C:\WINDOWS\Prefetch
5) ping C:\WINDOWS\ServicePackFiles\i386
6) PING winxp\I386

Sooo yeah. I have no idea who there are three pings(1,2,5), one weird ping called PING (6), and two pings in my prefetch. I can't really change the extensions on these (or I don't know how at least) either. All the pings work the same too: I open, it closes. I did a virus scan as well, and the computer detected no viruses.

Ping.exe is a command line tool; you can't run it on its own by double clicking. I suggest you rename all but 1 to something like 1ping 2ping etc. until you establish which the correct ping is.

You can also open a command window into the different folders that those ping files are in. Then, type in the file's name that you want to run and your cmd window will run it without suddenly closing.

In windows XP you can right click on the folder ping is in and select "open command prompt here". In 7 you can just right click in the folder while it's open and select "open command prompt here".

I can't give guarantees, but here's what I think:

1) leftover from installation - not needed
2) leftover from service pack installation - only needed if you want to undo the service pack, which will never happen
3) & 4) Caching information to load ping.exe faster. I suspect one is for the corrupted version, and one for the working one
5) updated version, installed by service pack
6) the original

I would leave 1) - 4) alone and try if 5) and 6) are working. (via open command prompt here)

To view and change file extensions you have to go to folder options in any explorer window (even search works), change to view tab and look for "hide extensions for known filetypes" and untick it.