Guide

The 7 Most Damaging Types of Ad Fraud in 2025 (And How to Fight Back)

By Naomi Kowalski

Reviewed by Senior Media Buyers

Ad fraud takes many shapes: click fraud, impression fraud, conversion fraud, ad stacking, domain spoofing, and more. The most harmful strains now use residential proxies and AI agents to bypass IP-based filters. A layered defence that includes managed click-fraud protection is vital.

1. Click Fraud: The Oldest and Most Persistent Threat

Click fraud means deliberately clicking on pay-per-click (PPC) ads with zero genuine interest in the product or service. It can happen manually (someone clicking over and over) or automatically (using bots and scripts). The aim is often to burn through a competitor's budget, inflate a publisher's revenue, or wreck campaign performance. Industry estimates suggest 14 to 25% of paid clicks could be invalid. Click fraud is especially rife on Google Performance Max and other automated campaigns where self-serve IP blockers can't work, because Google blocks third-party API access to PMax. Managed click-fraud protection services can spot and filter these clicks in real time, even when IP-based tools are in the dark.

2. Impression Fraud: Fake Views That Drain Display Budgets

Impression fraud generates fake ad impressions, often through hidden ad placements, pixel stuffing, or bot-triggered page refreshes. The advertiser pays for views that no human ever actually sees. A classic trick is ad stacking, where several ads are laid on top of each other in a single ad slot; only the top ad is visible, but all record an impression. Another version is pixel stuffing, where an ad sits inside a 1x1 pixel iframe. Telltale signs include sudden impression spikes paired with low engagement, high bounce rates, and mismatches between server-side and client-side tracking.

3. Conversion Fraud: Fake Leads and Sales

Conversion fraud goes after performance-based campaigns (CPA, CPL, CPS). Fraudsters use bots, click farms, or stolen user data to submit fake leads, sign-ups, or even purchases. This type is especially nasty because it looks like real conversions, complete with form fills, email verifications, and sometimes tiny transactions. Advertisers end up paying for worthless leads, messing up their attribution models, and making poor optimisation choices. Key red flags include unusually high conversion rates from a single IP or device, low-quality leads (like gibberish emails or disposable phone numbers), and a big chunk of conversions that never turn into paying customers.

4. Ad Stacking and Pixel Stuffing: Invisible Ads

Ad stacking crams multiple ads into one ad container, so only the top ad is seen by the user. Every ad in the stack registers an impression, but the advertiser pays for views that never really happened. Pixel stuffing is similar: an ad is squashed into a 1x1 pixel frame, invisible to the user, yet still counted as a view. These tactics often pop up on low-quality websites or in programmatic exchanges. Spotting them means checking viewability metrics (like Google Active View) and comparing impression counts against real user engagement. If viewability dips below 50% or impressions hugely outnumber unique users, ad stacking could be the culprit.

5. Domain Spoofing and Ad Injection

Domain spoofing (or ad fraud through misrepresentation) happens when a fraudster disguises a low-quality website as a premium publisher in the ad exchange. The advertiser thinks they're buying inventory on a reputable site like Forbes or The New York Times, but the ad actually runs on a dodgy or low-traffic site. Ad injection involves malware or browser extensions that sneak unauthorised ads into a user's browser, often swapping out legitimate ones. These fraud types are tough to catch without pre-bid verification tools or supply-path optimisation. Advertisers should lean on ads.txt and sellers.json to confirm authorised sellers.

6. Sophisticated Invalid Traffic (SIVT): Residential Proxies and AI Agents

SIVT is the most advanced form of ad fraud, using residential proxies, click farms, and AI-generated traffic to imitate human behaviour. Residential proxies route traffic through real home IP addresses, making it nearly impossible for IP-based blocklists to spot them. AI agents (sometimes called 'ad fraud bots 2.0') can mimic mouse movements, scroll patterns, and even session lengths. Recent reports show AI-agent traffic is growing about 78 times year over year. These attacks are especially dangerous for Performance Max campaigns because Google's own automated systems can be fooled by these sophisticated signals. Managed click-fraud protection services that rely on behavioural analysis and device fingerprinting can catch SIVT that IP blockers let through.

7. Competitor Click Fraud and Budget Exhaustion Attacks

Competitor click fraud is a deliberate attack where a rival clicks on your ads to use up your daily budget, so your ads stop showing early in the day. This is particularly common in competitive sectors like legal, insurance, and home services. The attacker might use a network of devices or a click farm to generate hundreds of clicks in a short time. Budget exhaustion attacks can also come from disgruntled affiliates or malicious publishers. Warning signs include a high number of clicks from one geographic area, clicks happening outside business hours, and a sudden drop in conversion rate after a spike in clicks. Real-time monitoring and automated click filtering can stop these attacks before they eat into your budget.

Frequently Asked Questions