NTFS Alternate Data Streams (or ADS in short) entry in Wikipedia:
Alternate data streams allows files to be associated with more than one data stream. For example, a file such as text.txt can have an ADS with the name of text.txt:secret.txt (of form filename:ads) that can only be accessed by knowing the ADS name or by specialized directory browsing programs. Alternate streams are not detectable in the original file's size but are lost when the original file (i.e. text.txt) is deleted with a RemoveFile or RemoveFileTransacted call (or a call that uses those calls), or when the file is copied or moved to a partition that doesn't support ADS (e.g. a FAT partition, a floppy disk, or a network share). While ADS is a useful feature, it can also easily eat up hard disk space if unknown either through being forgotten or not being detected.

So, in my example, C:\~:~ is a alternate data stream of c:\~ containing many times the SID. The file will grow until the disk is full.

lads.exe - Useful command line to list ADS:
http://www.heysoft.de/Frames/f_sw_la_en.htm

NB: On my computer (XP x64) when I kill kix32.exe I don't get logged off.