Free tool

IP reputation check

Found an address in your firewall log, in netstat, or in an email header? Check it against the six threat lists NetSecWall uses, and see who owns it.

What the lists are

FireHOL Level 1
A combined list built to be safe to block outright: known attack sources, malware hosts, and address ranges that should never appear on the internet.
abuse.ch Feodo Tracker
Botnet command-and-control servers for banking trojans and malware loaders.
Emerging Threats Compromised
Hosts that Proofpoint's Emerging Threats team has seen compromised and attacking others.
Spamhaus DROP
Networks hijacked by, or leased to, spam and cybercrime operations.
blocklist.de
Addresses reported in the last 48 hours for attacking servers: SSH, mail, FTP and web logins.
Tor exit nodes
Where Tor traffic leaves the Tor network. Shown, but not counted as a threat.

A listing is a reason to look, not a verdict. Shared hosting and content networks mean an ordinary site can sit next to a bad one. And an address on no list is not proof it is safe: new attack servers appear every day.