VeraCrypt is a free open source disk encryption software for Windows, Mac OSX and Linux. Brought to you by IDRIX (https://www.idrix.fr) and based on TrueCrypt 7.1a.
VeraCrypt main features:

Creates a virtual encrypted disk within a file and mounts it as a real disk.
Encrypts an entire partition or storage device such as USB flash drive or hard drive.
Encrypts a partition or drive where Windows is installed (pre-boot authentication).
Encryption is automatic, real-time(on-the-fly) and transparent.
Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.
Encryption can be hardware-accelerated on modern processors.
Provides plausible deniability, in case an adversary forces you to reveal the password: Hidden volume (steganography) and hidden operating system.
More information about the features of VeraCrypt may be found in the documentation

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