1. A method of limiting undesired messages within a social networking service, the method comprising: receiving, from a user of the social networking service, a message intended to be broadcast by the social networking service; synchronously analyzing the message, by a first computer processor, according to a set of characteristics of undesired messages, the set of characteristics stored in a database; asynchronously analyzing the message, by a second computer processor, including: analyzing the message according to a machine learning algorithm for detecting undesired messages, identifying a characteristic of the message, and adding the characteristic to the set of characteristics in the database for the synchronous analyzing; based on at least one of the synchronous analyzing and the asynchronous analyzing, determining that the message is unwanted; and restricting propagation of the message in the social networking service based on determining that the message is unwanted.