An MSSP (managed security service provider) is an Internet service provider (ISP) that provides an organization with some amount of network security management, which may include virus blocking, spam blocking, intrusion detection, firewalls, and virtual private network (VPN) management. An MSSP can also handle system changes, modifications, and upgrades.

MSSPs have evolved in various ways. Some traditional ISPs, noting the increasing demand for Internet security that has occurred in recent years, have added managed security to their repertoires. A few security vendors have added Internet access, thus becoming MSSPs. Still other MSSPs have come into existence as brand new entities.

An MSSP offers cost savings by allowing an organization to outsource its security functions. But some organizations are reluctant to give up complete control over the security of their systems. In addition, there may be considerable variability in competence among MSSPs