Modern web platforms, advertising, and social networks pour millions of dollars into anti-fraud. Their logic is simple: let live users with normal devices pass through, cutting off any suspicious or automated traffic.
Proxies, at the same time, are the standard tool for bypassing anti-fraud systems, used in multi-accounting, traffic arbitrage, and data scraping. Therefore, security systems look at them first and foremost.

In this article, we will analyze by what markers platforms figure out IP address spoofing, how to properly test proxies before launch, and what setup errors most often lead to the loss of an entire network of accounts.

Why websites and services block proxies

Proxy blocking is a defensive reaction of the server: it refuses to process requests coming from a specific IP address or subnet. Technically, this manifests itself in different ways. The server can return an error code (most often 403 Forbidden) or start chasing you in a circle through captchas like Cloudflare Turnstile or Google reCAPTCHA: you pass the check, and after a couple of clicks everything starts anew.

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There is also the most unpleasant option — a shadow ban. Outwardly, everything works as usual, nothing breaks. But in fact, you are simply cut off: pages load, actions seem to pass, but there is no result — content is not seen, data is not collected, the necessary actions do not reach the system.

Websites apply such harsh measures for several objective reasons.

Protection against scraping and DDoS attacks

Any large website is a source of various data: prices, contacts, content. When they begin to be massively scraped, the load on the server grows sharply. For example, hundreds or thousands of requests fly in a row from a single IP. To the system, this looks like the behavior of a robot.

Then the request limit triggers: first they cut the speed, then they can completely block the IP.

Combating multi-accounting and arbitrage

Social networks and advertising platforms build ecosystems based on the "one person — one account" concept. They need a clean audience because advertisers pay for impressions to live people, not bots or clones.

But in arbitrage, you cannot build systemic work with a single account. To drive traffic, you need dozens, if not hundreds, of accounts.
Anti-fraud systems understand this perfectly well and strictly monitor who is logging in and from where. If a platform sees that there is constant authorization into different accounts from a single IP address, it quickly links them together. As soon as algorithms find such a farm, everything happens very quickly after that: a chain block is launched, and the system takes down the entire network of accounts at once, indiscriminately.

Regional restrictions and content licensing

Streaming services, online stores, and payment systems are rigidly tied to regions: these are the requirements of licenses and local laws. Therefore, some content or features are simply unavailable outside the required country.

For payment systems, the control is even stricter: they check where you log in from and whether this matches the user data and the card. If the IP points to one country, and the card or profile to another, the system perceives this as a risk.

In such cases, the operation often simply does not go through: the transaction is rejected or immediately blocked.

How platforms identify proxy traffic

Security algorithms have long outgrown trivial matching of IP addresses against blacklists. Today, anti-fraud systems dig much deeper, capturing dozens of metrics both at the network level and directly from your browser.

Analysis of IP addresses

Every IP is tied to a specific provider or autonomous system. Most cheap proxies run on servers of popular data centers like Amazon AWS, DigitalOcean, or Hetzner. The problem is that ordinary people do not access the internet this way: they sit through home or mobile providers. As soon as anti-fraud sees a server IP, your risk level instantly skyrockets. Large platforms use powerful databases (for example, MaxMind) that determine in real-time whether the address belongs to a hosting service or a known proxy seller.

GEO and time zones

Through basic JavaScript functions, the site easily checks the local time on your device. Let's say you turned on a Vietnam proxy with the GMT+7 time zone, but the system time on the computer remained Moscow time (GMT+3). For anti-fraud, this four-hour gap signals a spoof. This also includes language mismatches: for example, if the IP is from Asia, but the browser requests pages in Russian in the Accept-Language headers.

WebRTC and DNS leaks

In the context of multi-accounting, WebRTC is a huge hole in anonymity. This technology establishes direct connections and knows how to query STUN servers, ignoring basic routing settings. If you sit through a default browser extension, the platform's anti-fraud sends a hidden request and easily extracts your real IP, despite the proxy.

With DNS leaks, the situation is similar. You can wrap all main traffic into a high-quality proxy, but out of habit, the browser will continue to send requests for decrypting domains to your local provider's servers. As a result, the anti-fraud system sees a suspicious picture: traffic is coming from an IP address, for example, in Vietnam, but communication nodes are for some reason being queried through a Russian provider. For reliable protection, regular extensions are not enough: specialized anti-detect solutions are needed here, for example, Linken Sphere.

Fingerprinting

Platforms collect a digital footprint of your device:

Canvas. The site asks the browser to render a geometric figure. Due to microscopic differences in graphics cards, drivers, and OS, each computer renders the picture with its unique pixel hash.
WebGL. Captures data on the exact model of the graphics processing unit and hardware acceleration by a similar principle.
Fonts and AudioContext. The system analyzes the list of installed system fonts and exactly how your sound card processes audio signals.

This entire array of data makes it possible to unmistakably identify a device even with a complete change of IP address. If the exact same unique footprint is exposed on ten accounts with different proxies, the platform will ban the entire network.

Passive analysis: network footprint conflict

Security systems are able to recognize spoofing at the most basic level by analyzing the structure of network packets. The fact is that each operating system forms TCP packets according to its own algorithm: they initially differ in time-to-live, window size, and other service markers.

A frequent error during setup is a mismatch between the declared and actual OS. For example, a user specifies a Windows 10 User-Agent in the browser, but routes traffic through a server proxy working on the basis of Linux.

When this traffic reaches the target website, the passive analysis system reads the headers of the packets themselves. Upon finding Linux signatures in them, the algorithm records a critical contradiction: the declared device profile does not match its network trace. For anti-fraud systems, such desynchronization serves as unequivocal proof that traffic was passed through a proxy server.

Behavioral factors and Trust Score: how algorithms figure out automation

Even an ideal technical footprint will not save if the account behaves unnaturally. A new IP from which mass registrations, ad launches, or active scraping immediately go out, initially does not inspire trust in the system.

Anti-fraud systems study behavior patterns. A live person acts non-linearly: he changes the scrolling speed, pauses when reading, moves the mouse unevenly, and navigates internal links.

Platforms track micromotor skills down to millisecond delays when entering text from the keyboard and unnaturally straight cursor trajectories. If actions are performed too evenly, monotonously, and according to strict timings, security scripts unmistakably classify the traffic as bot work and block the profile.

How to reduce the risk of blocking

The entire essence of bypassing blockings comes down to one simple rule: to anti-fraud you must look like a typical user who accesses the internet from a clean device via a regular provider.

Choosing the right proxy type

Cheap server proxies are suitable only for draft work, for example, scraping search engine results without authorization or collecting data from websites with weak security. There is no sense in going to advertising cabinets or working with payments with them: such IPs quickly drop off. For more serious tasks, completely different solutions are needed.

Residential proxies. These are the IPs of regular home devices: computers and Wi-Fi routers. To the system, they look like visits from regular users, for example, a subscriber to Rostelecom, Comcast, or Vodafone. Such traffic does not stand out from the general stream.

Mobile proxies. Cellular operators use CGNAT technology: they have millions of subscribers, and there are not enough free IPv4 addresses for everyone. Therefore, thousands of real people go online simultaneously from their smartphones via a single external IP address. Advertising platforms and social networks know about this, so they cannot send such an address to the black list.

Using anti-detect browsers

Specialized software is required to manage multiple accounts. Anti-detect browsers substitute the digital footprint at the browser core level.

Each profile in such a browser looks to security systems as a separate physical computer with its own unique hardware. It is important to use modern solutions that regularly update browser cores in accordance with Chrome releases (one of the leaders in update speed is Linken Sphere).

Precise profile configuration

Anti-detect settings must fully match the proxy parameters:

Time zone — matching the IP's geo.
System and browser language — for the same region.
GEO — the same city from where the connection originates.

If there are discrepancies, the system quickly records this.

Warming up accounts

An account with a history lives noticeably longer and withstands more active work, so it is warmed up first. The profile must behave like a regular user: visit sites, scroll pages, read content, sometimes register, leave an email, subscribe. Over time, cookies and traces of activity accumulate.

How to check proxies before launch

Launching profiles on unchecked IP addresses often leads to an instant block and loss of farming results. Before work, every new proxy must be tested by four parameters:

Fraud Score and IP cleanliness. Check the address via IPQualityScore or Pixelscan. If the risk indicator is above 50 or the system flags VPN, Tor, and Proxy, such a proxy will not pass strict anti-fraud.
WebRTC and DNS leaks. Services like Whoer.net help to identify leaks of real data. The geolocation of the DNS server must match the country of the proxy. The WebRTC protocol must broadcast the substitute IP address: disabling this feature entirely arouses suspicions of the algorithms.
Presence in spam databases. Make sure through monitors (e.g., Spamhaus) that the IP is not listed in global blacklists. If the address was previously used for spamming, the account will be blocked immediately after registration.
Speed and ping. Residential proxies often have a high ping — sometimes 500 ms and above. Because of this, pages and scripts load with delays, and to the system, this looks like unstable or unnatural work. The stability of the connection itself is also important. If the link drops during a process, like launching a campaign or logging into an account, the platform can send the profile for additional checking.

Frequent mistakes when working with proxies

Even a powerful anti-detect like Linken Sphere will not protect a network of accounts if logical errors are made when configuring network parameters:

Using server IPs for complex tasks. Attempting to launch ads or register new accounts in a social network through cheap data center proxies leads to a permanent ban. Algorithms read the hosting ASN and block the profile upon the first attempt to link a payment card.
Working through public free proxies. Such addresses are not only in all blacklists but are also often scam projects. Owners of free servers can intercept all passing traffic: logins, passwords, and bank card data.
Mismatch between the footprint and network type. If you use a mobile proxy but set a desktop User-Agent and a PC monitor resolution in the browser, the system will record an anomaly. A stationary computer with a wide screen connected via a mobile tower lowers the profile's trust.
A sharp change in geolocation. If an account worked through a European country's IP, and 5 minutes later authorizes from an Asian address, anti-fraud records suspicious activity. Between geolocation changes, you must pause for a time equal to a real flight between the countries.
Linking accounts. Connecting dozens of profiles to a single IP address leads to their union into a single cluster on the advertising platform's side. If one profile violates the rules, the platform will block the entire network.

Conclusion

Platforms block proxies to protect against scraping and multi-accounting, calculating the slightest anomalies in network packets, browser footprints, and behavior. For stable work, trusted mobile or residential IP addresses combined with a powerful anti-detect browser are necessary.