Embodiments herein relate to a method performed by a detecting node (101) in a communications network (100), for detecting that a wireless device, WD, (120) associated with a first domain of the communications network (100) has been communicating with a non-legitimate device (150). The non-legitimate device (150) is a device associated with a second domain of the communications network (100). The non-legitimate device (150) impersonates a network node (110, 111, 140) of a first domain of the communications network (100). The detecting node (101) obtains information regarding one or more protocol events related to the communication between the WD (120) and a first network node (110, 111, 140). The information comprises a time instance related to the one or more protocol events. The detecting node (101) determines, based on the time instance and a set of time limits related to the one or more protocol events, that the WD (120) has been communicating with the non-legitimate device (150).