Abstract: Security check method and apparatus reduces problems that can arise if the user security data set becomes known by unauthorized persons. To address this problem only part of the user data set is recorded in insecure sections of the system. For example, a security check preventing unauthorized remote access to a shared computer is provided by capturing a user data set representing a user's iris, operating the user's personal computer to select only a portion of the captured data set requested by the shared computer and transmitting the portion along a telecommunications line. The shared computer derives partial data sets from stored user data sets using a similar selection to that used by personal computer and compares the partial data set it has derived with the partial data set transmitted by the personal computer in deciding whether to grant access. Point-of-sale devices and cards recording only partial user data sets are also disclosed.