Providing social-network information to third-party systems

A first computing system associated with a social-networking system, comprising:

• a memory comprising instructions executable by one or more processors;
• and the one or more processors coupled to the memory and operable to execute the instructions, the one or more processors being operable when executing the instructions to:
• receive, from a second computing system associated with a third-party system, a query comprising a first identifier corresponding to a user of the third-party system, wherein the first identifier is computed by applying a hash algorithm to a user credential associated with the user of the third-party system, wherein the third-party system is separate from and external to the social-networking system, wherein the social-networking system comprises a graph comprising a plurality of nodes and edges connecting the nodes, wherein at least some of the nodes correspond to members of the social-networking system;
• determine whether the user of the third-party system matches a member of the social-networking system by comparing the first identifier with each of one or more second identifiers that each correspond to one of a plurality of members of the social-networking system, wherein the second identifier is computed by applying the hash algorithm to a user credential associated with the member of the social-networking system that the second identifier corresponds to;
• and
• if one of the second identifiers computed by applying the hash algorithm matches the first identifier computed by applying the hash algorithm, then transmit, to the second computing system associated with the third-party system, social-network information of the member of the social-networking system corresponding to the second identifier matching the first identifier in response to the query.