IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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S 5.79 Protection against call number identification
during use of mobile phones
Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Users
In the GSM network the number from which a call is being made can be
indicated to the recipient of a call. Whether this is in fact the case depends on
the technical equipment and the configuration of the mobile phones and/or at
the network provider's end.
It is possible to prevent one's own call number from being transmitted to the
person telephoned by using the call number suppression function on the
mobile phone (either for the next call or for all other calls). This option is
often found in mobile phone menus under menu option names such as
"Incognito" or "Anonymous".
Passing on of call number information can also be prevented on an ongoing
basis through the network provider.
If mobile phones and SIM cards are swapped around between users, this can
provide a certain protection against the association of call numbers with
particular persons, as it prevents a permanent association between user and
call number or between mobile phone and user from being deduced. However,
the link, for example, to an agency or company, will remain.
A particular person's mobile phone number can be ascertained not only
through transmission of the call number but also from public telephone
directories, if the number is entered there. When concluding a mobile phone
contract, the question of whether and in what form an entry should appear in
public telephone directories should therefore be carefully considered. The
same applies to the publication of call numbers in internal telephone
directories and to the disclosure of these in various applications where entry of
such data is requested (e.g. forms, prize draws etc.).
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IT-Baseline Protection Manual: Oktober 2000
Publication of phone
numbers