The NTFS file system provides applications the ability to create alternate data streams of information. By default, all data is stored in a file's main unnamed data stream, but by using the syntax "file:stream", you are able to read and write to alternates. Not all applications are written to access alternate streams, but you can demonstrate streams very simply. First, change to a directory on a NTFS drive from within a command prompt. Next, type "echo hello > test:stream". You've just created a stream named 'stream' that is associated with the file 'test'. Note that when you look at the size of test it is reported as 0, and the file looks empty when opened in any text editor. To see your stream enter "more < test:stream" (the type command doesn't accept stream syntax so you have to use more).
NT does not come with any tools that let you see which NTFS files have streams associated with them, so I've written one myself. Streams will examine the files and directories (note that directories can also have alternate data streams) you specify and inform you of the name and sizes of any named streams it encounters within those files. Streams makes use of an undocumented native function for retrieving file stream information. Full source code is included.
Usage: streams [-s] [-d] <file or directory>
Streams takes wildcards e.g. 'streams *.txt'.