BoxCryptor is basically a virtual hard disk that encrypts files on the fly using 256-bit AES encryption. Unlike TrueCrypt, another popular on-the-fly encryption tool, BoxCryptor encrypts individual files, not an entire volume or container. That means that your BoxCryptor-encrypted files sync with your cloud storage service immediately after you save them, whereas with TrueCrypt syncing occurs only after you finish encrypting an entire volume.