Alternate Data Stream (ADS)
Alternate Data Stream is a Windows NTFS technology to allow adding data-streams to files.
ADS is a useful technology, however has many limitations, at it only works in NTFS and hard to manage for administrators. It allows many useful attribution to files, but also can be misused to cover unwanted content.
Show ADS in a directory
With the CMD line interface:
dir /r
will list all files and will also show under each file if there is an ADS
Delete ADS
Here you need to use PowerShell. I did not (yet) find a solution to do it through command line (CMD).
In PowerShell the listing of all files with the /r parameter works like: cmd /r dir /r
Now to delete a particular data stream: delete-item .\filename.ext:data-stream