What it does
ShieldsUP! is GRC's Internet connection profiling service, which sends probes from its servers to the connection being examined.
ShieldsUP! sends probes from GRC toward the connection being examined, so its view is external to the LAN. GRC requires authority over the intervening equipment and explains that firewall logs may record these contacts. Its Port Authority documentation describes common-port tests, a 1056-port graphical view, custom sets of up to 64 ports or ranges, and copyable text summaries. That feature document is historical, last edited in 2003; confirm the available test before relying on an old port-set description. A result concerns the selected connection, probes and configuration at that time, rather than establishing the security of every service or device.
Strengths
- External perspective on the tested connection
- Explains expected firewall log entries
Watch out for
- Testing requires authority over the intervening network equipment
Sources
- GRC | ShieldsUP! — Internet Vulnerability Profiling (Oct 26, 2026)
- ShieldsUP Port Authority documented controls (Oct 26, 2026)