A big mess

From OS X Scientific Computing

The disk is read/write accessible by default, but the user's numerical uid (eg: 503) must be the same on both the host an client machine. (Be aware that if joe on the server has uid 503 and sarah on the client has uid 503, sarah will have read-write access to joe's files!) (OS X, and at least some GNU/Linux systems, assigns uid numbers sequentially to each new user, starting with 501. Other systems assign large random numbers, which makes the appearance of this sort of security anomaly (or hole) statistically much more unlikely.)