1. A method comprising: receiving a set of trusted user accounts at a computing device, wherein each trusted user account in the set of trusted user accounts is associated with its own vouching quota, and wherein the vouching quota associated with a trusted user account limits a number of untrusted user accounts that the trusted user account can vouch for; determining, by the computing device, a trusted user account from the set of trusted user accounts that is associated with an untrusted user account; determining whether the vouching quota associated with the determined trusted user account is greater than a vouching cost by the computing device; and when it is determined that the vouching quota is greater than the vouching cost, generating an indicator vouching for the untrusted user account by the computing device, wherein an amount of vouching quota associated with a trusted user account is based in part on a growth rate.