Yes. 3.99.158.157 is listed in the HProxy free proxy database as a public proxy, exiting from Montreal, Quebec, Canada. At least one port is responding right now.
A proxy on an IP address means that address is running a server that forwards other people’s traffic. When you route a request through it, the site you visit sees the proxy’s IP instead of yours. Public proxies like the ones in this database are open for anyone to use, which is exactly why they are useful for quick tests and equally why they are unreliable: they are shared by large numbers of strangers and run on infrastructure nobody is paid to maintain.
People look up whether a specific IP is a proxy for two main reasons. The first is to use it: you found 3.99.158.157 on a list and want to know if it is alive, what protocols it speaks, and where it exits before pointing a scraper or browser at it. The second is to defend against it: you run a site and want to know if traffic from 3.99.158.157 is coming through an open proxy, so you can decide whether to challenge or block it. This page answers both from the same data.
Whichever side you are on, remember that free, public proxies are unstable by nature. An IP that is alive right now can be dead within minutes, anonymity grades are best-effort rather than guaranteed, and popular addresses are often already rate-limited or blocked by large sites. Never send passwords, payment details or anything sensitive through a public proxy, and always verify an IP right before you depend on it. For work that has to keep running, dedicated or cleanly rotated paid proxies are the dependable alternative.
Yes. 3.99.158.157 appears in the HProxy free proxy database as a public proxy, with 72 open proxy ports (http, https, socks4, socks5). Free proxies come and go, so its live status is rechecked continuously and may change.
3.99.158.157 was seen speaking http, https, socks4, socks5 on ports 569, 1080, 1288, 3128, 3169, 3518, 3756, 4000, 4020, 4760, 4895, 5041, 6304, 6334, 6489, 7154, 8118, 8506, 8542, 9294, 9763, 10363, 11714, 13900, 17449, 17543, 20714, 20878, 21099, 23397, 23611, 25033, 25638, 26357, 26643, 27494, 28629, 30741, 31675, 32117, 33074, 33276, 34065, 34833, 35170, 37917, 39393, 39552, 39586, 41425, 43033, 43756, 45149, 45893, 47594, 48024, 48140, 48243, 49518, 50048, 50606, 53972, 54001, 54722, 54809, 55205, 55815, 56561, 58080, 58242, 58404, 59908. HTTP and HTTPS proxies carry web traffic; SOCKS4 and SOCKS5 carry any TCP traffic.
Treat it with caution. It is a public proxy that anyone can route through, so never send passwords, payment details or other sensitive data through it. Free proxies are fine for low-stakes testing, but for anything serious use a trusted paid provider.
Free proxies are shared by many users and run on infrastructure no one is paid to maintain, so they get overloaded, rate-limited or shut down constantly. An IP that is alive now can be dead within minutes. Always verify right before you rely on it.
If you run a site and want to block this proxy, deny the IP at your firewall, WAF or application layer. Because free proxy IPs change constantly, blocking individual addresses is a moving target, so most teams use a continuously updated proxy and abuse database rather than a static blocklist.
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