1. What are dynamic IP addresses?
Unlike a static IP address, a dynamic IP address does not, in principle, make it possible to
establish a link between a specific computer and the physical network connection, using files,
which are accessible to the public. Indeed, a dynamic IP address changes with each new connection
to the Internet.
Dynamic IP addresses change with each new connection to the Internet
However, in certain circumstances, with the help of additional information, it is possible to
establish the identity of the owner of the computer linked to the IP address, via a dynamic IP
The question therefore arose whether a dynamic IP address should not be regarded as personal
data in the sense of the Privacy Directive?
2. The proceedings before the German Federal Court
The German Federal Court submitted this matter to the Court by means of prejudicial questions.
The reason for this was proceedings brought by a German citizen against the Federal Republic of
Germany, following his visit of German federal institution websites. The German citizen demanded
that the German authorities would be prohibited to save the IP-address of the hosting system from
where he accessed the websites of the German federal institutions.
It appeared that most of these websites registered the IP addresses of each visit in log files, to
protect against cyberattacks and to permit prosecution of possible attackers. Following the visit,
these log files contain the IP address of the computer from which the website was visited.
Given that the German citizen could not accept the conduct of the German authorities, he lodged an
appeal against this kind of storage. His appeals was aimed to have the Federal Republic of Germany
banned from storing or having third parties store the IP address of the host system from which the
internet user gained access to the publicly-accessible online media websites of German federal
institutions, in as much as the storage of that IP address is not required in order to restore
availability of that media in the event of an interruption.
The appeal was dismissed in first instance. However, the Appeal Judge granted part of the request.
The judge obliged the Federal Republic of Germany to desist from storing IP addresses or having
them stored after the session, if the address is stored together with the time of the visit
occurring via this address, and if the user revealed his identity during his visit.
In other words, the appeal judge decided that a dynamic IP address can be regarded as personal
data, if it is stored together with the time of the visit via this address, and the user revealed
his identity during his visit.
Indeed, this allows the website operator to identify the visitor by linking the visitor’s name with
his IP address.
3. Prejudicial questions of the Federal Court
An appeal was also lodged against this decision. The German citizen felt that the appeal judge’s
decision did not go far enough, and the German Federal Republic felt that this decision went much
The Federal Court explained that the dynamic IP addresses of the computer of a user, which are
stored by the operator of online media services, together with other stored log files, constitute
specific data concerning the material circumstances of a visitor.
After all, this data provides information regarding the fact that the visitor visited specific
websites, or retrieved specific files, at specific times via the Internet.
However, in principle, this data does not make it possible to directly identify a person.
It is only possible to identify the visitor in question when the operator of the website or on-line
media service receives information from the Internet provider concerning the user’s identity.
The Federal Court then asked the European Court of Justice a prejudicial question concerning the
interpretation of the provisions of the Privacy Directive.
Article 2, a) of the Privacy Directive defines personal data as: any information relating to an
identified or identifiable natural person ("data subject"). an identifiable person is one
who can be identified, directly or indirectly, in particular by reference to an identification
number or to one or more factors specific to his physical, physiological, mental, economic,
cultural or social identity;
The Court had to answer the question whether pursuant to this Article 2, a) a dynamic IP address
that is registered by an on-line media service operator, each time a person visits a website, is
personal data, if only a third party, such as an internet provider, holds the additional
information required to identify that person.
4. How did the Court of Justice judge?
The Court observed that a dynamic IP address in itself is not personal data, as the identity of
the person owning the computer from whom the website was visited is not immediately apparent from
However, the Court also had to verify whether a dynamic IP address can be regarded as personal data
if it relates to identifiable persons and the additional information required to identify that
person is held by a third party.
The term “identifiable” presumes not only direct identification, but also indirect identification
Indeed, the term “identifiable” presumes not only direct identification, but also indirect
identification. From the use of the term “indirect” in the definition of personal data, the Court
deduces that it is not necessary for the data itself to allow the person to be identified, in order
for it to qualify as personal data.
Determining whether a person is identifiable, requires examining all means which may reasonably be
assumed to be used by the party responsible for processing or by any other person in order to
identify the party in question.
The Court stated that there is no requirement for all the information, which can be used to
identify the person to be stored by one and the same person.
This means that the fact that the website operator does not hold the additional information which
is required in order to identify the user of a website does not preclude dynamic IP addresses,
registered by the website operator, from being regarded as personal data.
It appears to the Court to be established that the possibility to combine a dynamic IP address with
additional information, which is not in the possession of the internet provider, constitutes a
means that may reasonably be assumed to be used in order to identify the person in question.
Therefore, in these circumstances, a dynamic IP address is personal data.
On the basis of this ruling, there is no longer any doubt as to the classification of dynamic IP
addresses. The Court has explicitly judged that dynamic IP addresses qualify as personal data, even
though the additional information which is required in order to identify the party in question is
held by a third party.
As a consequence, website operators which store dynamic IP addresses in their log files, must
respect the provisions of the Privacy Directive and soon the GDPR.