There are at least three possible ways.
1) Aliases:  Doskey ls=dir
2) A replacement for the Windows cmd.exe file
3) Binary edit and change the cmd.exe file.

The first (aliases) is not very likely.

The second is possible (cygwin or similar replacement for the cmd.exe file).
(look for a different date and file size for the cmd.exe file)
cmd.exe is located in C:\Windows\system32 and the exact size when checking
the file properties is 388,608 bytes
Should you find that the file size has changed there is another copy of
cmd.exe located in the C:\WINDOWS\ServicePackFiles\i386 folder, double click
on this file and see if the results are back to normal.

It takes a skilled person with the right tool to perform a binary edit of
cmd.exe and make it work, however if they did this the 'Date Modified'
attribute would be a very recent date.

JS