## 1 Introduction  
The major goal of an intrusion detection system (IDS) is to identify any signs of suspicious activities in either systems or networks [1]. IDSs are widely adopted in various organizations and can be generally classified into two groups: _host-based IDSs (HIDSs)_ and _network-based IDSs (NIDSs)_. The HIDS identifies malicious events for an end system or application by monitoring local events and states. The NIDS focuses on network environments and detects potential attacks by monitoring and examining traffic outside the demilitarized zone (DMZ) or within an internal network [2]. Further, there are usually two major detection methods for a typical IDS, namely, the signature-based detection approach and the anomaly-based detection approach. A signature-based IDS detects suspicious events by comparing incoming payloads with stored signatures (called rules), while an anomaly-based IDS detects malicious events through identifying significant deviations between the current behavioral profile and the normal behavioral profile. A normal profile is used to describe the characteristics of applications and connections via monitoring for a period of time [1]. With the increasing complexity of current intrusions, it is found that a single or isolated IDS would not work effectively in a complicated scenario [3; 4]. These attacks may cause great damage if they cannot be detected timely; that is, they may cause the entire network to be paralyzed. With the purpose of improving the detection accuracy of single IDSs, research has been made for collaborative intrusion detection networks (CIDNs), which enable different IDS nodes to collect and exchange data with each other [4]. The collaborative nature of CIDNs can help to optimize the capability of an IDS; however, insider attacks are one great threat that can significantly degrade the security level of the whole network [3]. As a result, there is a need to implement additional mechanisms to protect a collaborative environment itself. Building appropriate trust-based mechanisms is a promising solution to protect CIDNs against insider threats. For this purpose, [PERSON] et al. [5] developed a kind of challenge-based trust mechanism (or _challenge mechanism_) for CIDNs, which utilizes _challenges_ to evaluate the reputation of IDS nodes. A challenge may contain some predefined alarms requesting the target node to rank the severity. Because the testing node generates the challenge (i.e., extracting from its database), it knows the alarm severity in advance. The reputation of an IDS node can be judged according to the satisfaction level between the expected answer and the received feedback. A line of relevant studies (e.g., [5; 6; 7]) have proven that the challenge mechanism can be robust against common insider attacks, like collusion attacks, in which several adversarial nodes work together to provide fake alarm information to target nodes, aiming to degrade the detection effectiveness. **Motivations. ** The challenge mechanism has shown good performance against common insider attacks, but it depends heavily on two major assumptions: (1) it is hard for an IDS node to distinguish between a challenge and a normal message; (2) malicious nodes would always send untruthful feedback. In a practical implementation, these two assumptions are not realistic in most cases, as adversarial nodes can behave in a much more dynamic and complicated way [8; 9]. As a result, because of these assumptions, challenge mechanisms may become problematic under some advanced attacks. As an example, [PERSON] et al. [8] designed an advanced attack, named the _passive message fingerprint attack_ (PMFA), which could help to distinguish between a challenge and normal messages. Under the PMFA, an IDS node can send untruthful answers to normal requests without decreasing their trust values. **Contributions. ** In this work, our motivation is to investigate the influence of a special on-off attack (SOOA), which is able to behave normally to one node while sending untruthful answers to another node.