human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "a case of collusion a study of the interface between ad libraries and their apps"
  Abstract: A growing concern with advertisement libraries on Android is their ability to exfiltrate personal information from their host applications. While previous work has looked at the libraries' abilities to measure private information on their own, advertising libraries also include APIs through which a host application can deliberately leak private information about the user. This study considers a corpus of 114,000 apps. We reconstruct the APIs for 103 ad libraries used in the corpus, and study how the privacy leaking APIs from the top 20 ad libraries are used by the applications. Notably, we have found that app popularity correlates with privacy leakage; the marginal increase in advertising revenue, multiplied over a larger user base, seems to incentivize these app vendors to violate their users' privacy.

Connected through hyperedge HE-1 (induced by source paper "android inter app communication threats and detection techniques"):
  with members:
    - "towards automated android app collusion detection"
    - "android security framework enabling generic and extensible access control on android"
    - "cross site scripting attacks on android webview"
    - "adsplit separating smartphone advertising from applications"
    - "dexpler converting android dalvik bytecode to jimple for static analysis with soot"
    - "quire lightweight provenance for smart phone operating systems"

Connected through hyperedge HE-2 (induced by source paper "demo recon revealing and controlling pii leaks in mobile network traffic"):
  with members:
    - "haystack a multi purpose mobile vantage point in user space"
    - "automated test input generation for android are we there yet"

Connected through hyperedge HE-3 (induced by source paper "mobileappscrutinator a simple yet efficient dynamic analysis approach for detecting privacy leaks across mobile oss"):
  with members:
    - "on the unicity of smartphone applications"

Connected through hyperedge HE-4 (induced by source paper "an empirical study of mobile ad targeting"):
  with members:
    - "i always feel like somebody s watching me measuring online behavioural advertising"
    - "adscape harvesting and analyzing online display ads"
    - "xray enhancing the web s transparency with differential correlation"
    - "longitudinal analysis of android ad library permissions"
    - "adsplit separating smartphone advertising from applications"

Connected through hyperedge HE-5 (induced by source paper "an investigation into the use of common libraries in android apps"):
  with members:
    - "dexpler converting android dalvik bytecode to jimple for static analysis with soot"
    - "smote synthetic minority over sampling technique"

Connected through hyperedge HE-6 (induced by source paper "privacy leakage in mobile computing tools methods and characteristics"):
  with members:
    - "privacy in sensor driven human data collection a guide for practitioners"
    - "i know what leaked in your pocket uncovering privacy leaks on android apps with static taint analysis"
    - "longitudinal analysis of android ad library permissions"
    - "participatory privacy enabling privacy in participatory sensing"
    - "adsplit separating smartphone advertising from applications"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.CR(Cryptography and Security)