Detecting malicious behaviour in participatory sensing settings

Security is crucial in modern computer systems hosting private and sensitive information. Our systems are vulnerable to a number of malicious threats such as ransomware, malware and viruses.  Recently, a global cyberattack (ransomware) affected hundred of organisations, most notably the UK’s NHS.  This malicious software “locked” the content stored on organisations’ hard drives, requiring money (to be paid in bitcoins) to “unlock” it and make it available back to their owners. Crowdsourcing (the practice of obtaining information by allocating tasks to a large number of people e.g. Wikipedia) is not immune of malicious behaviour. On the contrary, the very openness of such systems make them ideal for malicious users to alter, corrupt or falsify information (data poisoning). In this post, we present an environmental monitoring example, where ordinary people take air quality readings (using mobile equipment) to monitor air pollution of their city or neighbourhood (see our previous post for more details on this example). Arguably, some people participating in such environmental campaigns can be malicious. Specifically, instead of taking readings to provide information about their environment,  they might deviate by following their own secret agenda. For instance, a factory owner might alter the readings showing that their factory pollutes the environment. The impact of such falsification is huge as it basically changes the overall picture of the environment, which in turn leads authorities to wrong actions regarding urban planning.

We argue that Artificial Intelligence (AI) techniques can be of great help in this domain. Given that measurements have a spatio-temporal correlation, a non-linear regression model can be overlaid over the environment (see previous post). The tricky part however is to differentiate between truthful and malicious readings. A plausible solution is to extend the non-linear regression model by assuming that each measurement has an individual and independent noise (variance) from each other (heteroskedasticity). For instance, a Gaussian Process (GP) model can be initially used and then extended to Heteroskedastic GP (HGP). The consequence of this action is that this individual noise can indicate the deviation of each measurement compared to the truthful measurements, which can either be attributed to sensor noise (which is always present in reality) or in malicious readings. An extended version of HGP, namely Trust-HGP (THGP), assigns a trust parameter to the model that captures the possibility of each measurement being malicious between the interval of (0,1).  The details of the THGP model as well as how it is utilised in this domain will be presented end of October at the fifth AAAI conference on human computation and crowdsourcing (HCOMP 2017). Stay tuned!

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