It's not an actual file, it's unmarked in the free space of the first volume. If you mount only the first volume, it will appear normal, and data loss will occur if more space is used.
Also, as jchw mentioned above, the headers are indistinguishable from random data already, and truecrypt supports full volume encryption already. This nesting feature is on top of the "volume looks like random data" feature.
https://www.truecrypt71a.com/documentation/plausible-deniabi...
Also, as jchw mentioned above, the headers are indistinguishable from random data already, and truecrypt supports full volume encryption already. This nesting feature is on top of the "volume looks like random data" feature.