How to encrypt your cloud storage for free

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.

via How to encrypt your cloud storage for free.