1. A method performed by a network node for detecting a false base station in a communications network, the method comprising:
sending a first message to a network device, which first message comprises first configuration data configuring the network device to perform measurements in order to collect first information transmitted by network nodes in a surrounding area of the network device,
receiving a first measurement report from the network device according to the first configuration,
sending a second message to the network device configuring the network device to collect secondary information,
receiving the secondary information from the network device,
detecting the presence of a false base station based on a difference between the received secondary information and predetermined target information.
2. The method according to claim 1, wherein the method performed by the network node further comprises:
comparing the received secondary information with predetermined target information in order to detect differences between the secondary information and the predetermined target information.
3. The method according to claim 2, wherein the method performed by the network node further comprises:
detecting a difference between the received first information and predetermined target information that is different than the target information to which the secondary information is compared.
4. The method according to claim 3, wherein the difference between at least one of the first information and the secondary information and the respective target information is detected based on the difference of the pilot signal strength.
5. The method according to claim 3, wherein the difference between at least one of the first information and the secondary information and the respective target information is detected based on a presence of a cell identity in the received information which is not present in the target information.
6. The method according to claim 3, wherein the difference between at least one of the first information and the secondary information and the respective target information is averaged over a plurality of network devices, and/or over a plurality of measurements made by a single network device, and/or over a plurality of measurements made by a plurality of network devices.
7. The method according to claim 2, wherein the comparison may comprise verifying that a given cell identifier and Cell Global Identity in the secondary information are assigned to the same Tracking Area Code or Location Area Code as in the secondary target information.
8. The method according to claim 1, wherein at least one of the first information and the secondary information comprises physical cell identifiers, carrier frequencies and pilot signal strengths.
9. The method according to claim 1, wherein at least one of the first information and the secondary information is collected from frequencies and radio technologies not used when the network node and network device communicate themselves.
10. The method according to claim 1, wherein the target information is cell planning data.
11. The method according to claim 1, wherein the secondary information is a System Information Block.
12. The method according to claim 1, wherein the network node configures the network device to perform measurements based on a Minimization to Drive Test function.
13. The method according to claim 1, wherein the network node configures the network device to perform measurements using an Automatic Neighbor Relation function.
14. The method according to claim 1, wherein the configuration is triggered by an event, which event is a handover or a detection of a pilot signaling strength exceeding a threshold value.
15. A network node for use in detecting a false base station in a communications network, wherein the network node is configured to:
send a message to a network device, which message comprises configuration data for configuring the network device to perform measurements in order to collect information transmitted by network nodes in a surrounding area of the network device;
receive a measurement report from the network device according to the configuration, wherein the measurement report comprises a physical cell identifier (PCI) that the network device determined from synchronization signals received by the network device, wherein the synchronization signals were transmitted by a base station;
determine whether the base station is a false base station based on the PCI reported by the network device; and
provide an indication that a false base station is present as a result of determining that the base station is a false base station.
16. The network node according to claim 15, wherein the network node is configured to determine whether the base station is a false base station based on the PCI reported by the network device by performing a process comprising determining whether the PCI reported by the network device is included in a list of PCIs maintained by the network node.