third-party.com Placeholder Domain Now Serves ClickFix Malware

The domain third-party.com, long used as a generic placeholder in software documentation and code examples, has been registered by attackers and is now serving a ClickFix lure to Windows browsers while showing a harmless page to everyone else. Manifold Security's Head of Research, Ax Sharma, explained that third-party.com has played the same role as example.com for years, but unlike example.com, which is reserved by the Internet Assigned Numbers Authority (IANA) for documentation, third-party.com was never reserved. Anyone could register it, and someone did. Every document, test case, or AI agent skill that hard-coded the domain now points readers at attacker-controlled infrastructure.

At the time of writing, the domain is flagged as malicious and unsafe on both VirusTotal and Google's Safe Browsing list. ClickFix is a social engineering attack that uses fake error messages, browser alerts, or CAPTCHA verification prompts to trick people into copying and running hidden commands. The pages often use clipboard hijacking, also called pastejacking, to automatically place a malicious command on the visitor's clipboard. The person is then told to paste it into the Windows Run dialog or macOS Terminal, believing they are fixing a problem. In reality, the command hands control to the attacker.

According to Manifold Security, the domain has been serving the ClickFix lure since at least June 2026. Windows users who visit the page see a fake Cloudflare check that poisons the clipboard and instructs them to paste and run a command through the Windows Run dialog. The pasted command is designed to download and execute a remote PowerShell payload, a scripting tool built into Windows that can run commands and install software. macOS users get a different response: the fake verification prompt shows an error that says macOS is not supported and tells them to try again from a Windows device.

A search on GitHub shows the domain is referenced in more than 1,700 public repositories, including documentation for AI agent skills and MCP servers that use third-party.com as an example endpoint. An MCP server is a helper service that AI assistants and agents can call to perform tasks, and developers often use placeholder domains in their examples. Sharma said that in every one of those places, the domain was exactly what it looked like: a placeholder, an example, a stand-in, and an entirely reasonable use by the teams involved. But it is now also a live pointer to a ClickFix server. This weaponization of a blindly trusted domain can open up avenues for prompt injection, where harmful instructions are inserted into the prompts an AI assistant or agent follows, leading to unintended behavior.

Manifold Security later said it identified 13 more placeholder domains that are not IANA reserved. Two of them, yoursite.com and your-domain.com, serve scams and scareware to macOS visitors, while showing an ordinary parking page to other users. The full list of domains that pass static checks is: your-domain.com, yourdomain.com, your-site.com, yoursite.com, your-app.com, yourapp.com, myapp.com, mysite.com, acme.com, company.com, mycompany.com, vendor.com, and foo.com. Security researcher Cody Nash reported that on a macOS browser, your-domain.com displayed a fake MacOS Security Center claiming the machine had four viruses and selling a counterfeit McAfee renewal at 55 percent off. On another macOS render, yoursite.com showed a counterfeit ZDF news article advertising an investment scheme.

The two scam and scareware sites appear in hundreds of thousands of GitHub files and hundreds of agent skills, according to Nash. Scareware and investment fraud may be less dangerous than clipboard malware, but the exposure they ride on is far larger, and none of it showed up in any static check Manifold ran. A static check is an automated scan that examines files without executing them, and it cannot see what a website decides to send only when a visitor arrives. Manifold pointed out that a developer can scan a skill, read a file, and resolve the domain from an analysis box and conclude it is fine, but be completely wrong about what a Windows user's agent receives when it follows the same link. The tell only appears at request time, from the caller that matters.

To counter the threat, developers and documentation owners should audit their documentation and treat non-reserved placeholder domains such as yourcompany.com, mycompany.com, your-api.com, and their lookalikes as squattable and open to abuse. Threat actors can register these domains and serve malicious content at any time. The recommended practice is to use only reserved placeholders like example.com, example.org, or example.net, and to avoid plausible-sounding domains that are not under your control. For website owners and IT teams, AEU DNS offers a private, secure DNS service, but this story shows why the defense must begin in the documentation itself: replace any unreserved placeholder domain with a reserved one you trust.