The free, open-source 7-Zip program compresses numerous files and folders into a single archive file that’s easily transferable. If the compressed files weren’t previously compressed, such as text files, the resulting archive will be considerably smaller than the sum of each file size. However, if the files were already compressed, such as JPG images or MPG movies, you won’t conserve much space by compressing them further. But, that’s only one of the benefits of compression, and honestly, if that’s all you were after, then Windows 8’s built-in ZIP support would suffice.
One of the features that sets 7-Zip apart from Windows’ integrated ZIP utility is archive encryption, which optionally applies strong, 256-bit AES encryption to the archive. This means as long as you’ve chosen a strong password, nobody can gain access to those files without the appropriate password, even if the archive is intercepted during email transit.
When applying encryption with 7-Zip, you have two file choices: 7Z or ZIP. The ZIP format supports AES-256 or ZipCrypto encryption methods. ZipCrypto is weaker than AES-256 and may be subject to attacks, but it has the advantage of being compatible with Windows, so a recipient could open the file without needing 7-Zip himself. Using the stronger AES-256 encryption method, however, would require 7-Zip, WinZip or other supporting software to open the archive. Alternatively, the 7Z format only offers the AES-256 encryption method, but has the additional advantage of optionally encrypting file names. Therefore, if you don’t want to reveal any information about your files, you should choose the 7Z format.