Is it possible to compress files from hundreds of megabytes to few megabytes?
Usually not. It can be done, but only if the data being compressed isn't very differential. This means you can compress text with good a ratio (there are only 26 lower-case characters, 26 upper-case characters and 10 numbers plus a few standard symbols like '!@#$...',and usually no more than 64 different symbols in standard text, but every symbol is saved using 8 or 16 bits, which gives 256 or 65536 combinations per symbol), but you cannot compress graphics or music very well.
KGB Archiver is the compression tool with an unbelievably high compression rate. Unfortunately, in spite of its powerful compression rate, it has high hardware requirements (I recommend processor with 1,5GHz clock and 256MB of RAM as an essential minimum). One of the advantages of KGB Archiver is also AES-256 encryption which is used to encrypt the archives. This is one of the strongest encryptions known for man.
Download Link : http://kgbarchiver.net/?page=download