Abstract: In some aspects, a computing system is configured to use graph-based techniques to detect synthetic identities. The computing system can generate a collection of graphs based on account data and transaction data for online entities. The collection of graphs includes multiple graph communities, each graph community including nodes and edges. Each node represents a user and an edge between a first node and a second node indicates a user represented by the second node is an authorized user of the user represented by the first node. The computing system can identify a clique graph community in the collection of graphs and compare the identified clique graph community with a known clique graph community that includes synthetic identities. The computing system can determine nodes in the identified clique graph community to be synthetic identities based on determining that the identified clique graph community is equivalent to the known clique graph community.