Definition
An MSSP, or managed security service provider, is a company that runs security operations for its clients on an ongoing basis. Services often include monitoring, threat detection, incident response and managing security tools. Clients pay a recurring fee instead of building their own security team.
The line between an MSP and an MSSP is not always clear. Many MSPs now offer security services, and some MSSPs also handle general IT. Companies use the labels differently.
MSSPs often choose vendors based on how well a product fits into their operations center, how it handles many clients at once and how pricing works at scale.
In practice
An MSSP adds a vendor's detection tool to its 24/7 monitoring service and bills clients a monthly fee that covers both the tool and the analysts.