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Reallocated Sectors 
Some storage devices, such as hard drives, internally reallocate/remap bad sectors. Whenever the 
device detects a sector to which data cannot be written, it marks the sector as bad and remaps it to 
a sector in a hidden reserved area on the drive. Any subsequent read/write operations from/to the 
bad sector are redirected to the sector in the reserved area. This means that any existing data in 
the bad sector remains on the drive and it cannot be erased (overwritten with other data). This may 

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have various security implications. For instance, data that is to be encrypted in place may remain 
unencrypted in the bad sector. Likewise, data to be erased (for example, during the process of 
creation of a hidden operating system) may remain in the bad sector. Plausible deniability (see 
section Plausible Deniability) may be adversely affected whenever a sector is reallocated. 
Additional examples of possible security implications are listed in the section Security 
Requirements and Precautions. Please note that this list is not exhaustive (these are just 
examples). Also note that TrueCrypt cannot prevent any security issues related to or caused by 
reallocated sectors. To find out the number of reallocated sectors on a hard drive, you can use e.g. 
a third-party software tool for reading so-called S.M.A.R.T. data. 
Defragmenting 
When you (or the operating system) defragment the file system in which a file-hosted TrueCrypt 
container is stored, a copy of the TrueCrypt container (or of its fragment) may remain in the free 
space on the host volume (in the defragmented file system). This may have various security 
implications. For example, if you change the volume password/keyfile(s) afterwards, and an 
adversary finds the old copy or fragment (the old header) of the TrueCrypt volume, he might use it 
to mount the volume using an old compromised password (and/or using compromised keyfiles that 
were necessary to mount the volume before the volume header was re-encrypted). To prevent this 
and other possible security issues (such as those mentioned in the section Volume Clones), do 
one of the following: 
• Use a partition/device-hosted TrueCrypt volume instead of file-hosted. 
• Securely erase free space on the host volume (in the defragmented file system) after 
defragmenting. 
• Do not defragment file systems in which you store TrueCrypt volumes.