IPAbuseCheck: Clients Abusing Web Proxies

Zscaler's IPAbuseCheck provides a free web interface and database of unauthenticated client IPs observed attempting to forward abusive or unwanted traffic through open proxies (20K+ IPs since July). The service catalogs patterns of abuse—such as brute-force web logins, SEO and forum spam, bulk registrations, and scraping—captured from unauthenticated proxy transactions to help ISPs and security professionals identify infected or malicious clients, while noting potential false positives and a focus on proxy-origin visibility rather than server-side denylists.