1. A method comprising: receiving at a network protection system a first alert from a first intrusion detection system associated with a first protected network, wherein the first alert is triggered by first network traffic that is evaluated by the first intrusion detection system and that is determined to match a first signature that is associated with undesired network behavior; receiving at the network protection system a second alert from a second intrusion detection system associated with a second protected network, wherein the second alert is triggered by second network traffic that is evaluated by the second intrusion detection system and that is determined to match the first signature; determining a source of the network traffic that triggered the first alert and the second alert; grouping at the network protection system the first alert and the second alert into an alert group based upon a common characteristic between the first alert and the second alert; assigning a determination to the alert group, the determination indicating a threat level associated with the alert group; generating an entry in an undesired source database based on the alert group, the entry comprising a first Internet Protocol (IP) address associated with the first alert; and providing the undesired source database to the first intrusion detection system and to the second intrusion detection system, such that the first intrusion detection system and the second intrusion detection system are configured to block network traffic that originates from the first IP address.