This tool removes blocks of 0x00 from files by replacing them with 
phantomblocks. That way, a file uses less diskspace while its contents 
hasn't changed at all!

BEWARE: after copying these files with tar, cp, cpio or any other tool, 
the phantomblocks have been replaced with 0x00-blocks again!

EXAMPLE: 

find / -type f -print | xargs -n 1 phantom -r -i

This would go trough the whole harddisk, scan all files and generate 
0x00-blocks where necessary.

WWW: http://www.vanheusden.com/Linux/phantom.php