Several organizations maintain and publish free blocklists of IP addresses and URLs of systems and networks suspected in malicious activities on-line. Some of these lists have usage restrictions:

The lists differ in format, goals, and data collection methodology. Be sure to read about the list before making use of it. Did you notice any blocklist sources that should be on this list, but are missing? Let me know. My other lists of on-line security resources outline Automated Malware Analysis Services and On-Line Tools for Malicious Website Lookups.

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