Method for detecting fraudulent users in a marketplace system

A server computer system for detecting fraudulent users in a marketplace system, comprising:

• a radio interface;
• a memory interface;
• and
• a processing unit configured to:
• generate a graph, wherein users are represented as nodes of the graph and two nodes are connected by an edge if the user represented by one of the nodes has used at least one marketplace system element which was also used by the user represented by the other of the nodes in the marketplace system and each node is associated with a feature set including information about behaviour of the user who is represented by the node in the marketplace system and structure information about a subgraph of the graph to which the node belongs;
• process the graph by a graph convolutional neural network configured to generate a score for each node of the graph;
• and
• detect one or more fraudulent users using the scores.

A non-transitory computer-readable medium comprising program instructions, which, when executed by one or more processors, cause the one or more processors to perform a method for detecting fraudulent users in a marketplace system, comprising:

• generating a graph, wherein users are represented as nodes of the graph and two nodes are connected by an edge if the user represented by one of the nodes has used at least one marketplace system element which was also used by the user represented by the other of the nodes in the marketplace system and each node is associated with a feature set including information about behaviour of the user who is represented by the node in the marketplace system and structure information about a subgraph of the graph to which the node belongs;
• processing the graph by a graph convolutional neural network configured to generate a score for each node of the graph;
• and
• detecting one or more fraudulent users using the scores.