Definition
Referrer Spam (or Ghost Traffic) is a spam technique that sends fake HTTP requests with a forged 'Referer' header to websites, or directly injects fake data into Google Analytics via the Measurement Protocol. The goal is to appear in site owners' referral traffic reports, who then curiously visit the spammer domain to find out where the traffic is coming from. There are two main types: 'crawler referrer spam' that actually visits the site with a fake referrer, and 'ghost referrer spam' that sends data directly to Google Analytics without ever visiting the site. Ghost spam exploits the fact that GA tracking IDs (UA-XXXXXX) are often predictable. Consequences include polluted Analytics data (bounce rate, sessions, pageviews), marketing decisions based on false data, and potential exposure to malicious sites. Solutions include GA filters (exclude invalid hostnames, known referrers), .htaccess to block spam crawlers, and migration to Google Analytics 4 which is more resistant to ghost spam.
Key Points
- Generates fake referral sessions in Google Analytics to attract site owners to spam sites
- Two types: crawler spam (real visit with fake referrer) and ghost spam (injected data without visit)
- Pollutes Analytics data and distorts marketing metrics (bounce rate, sessions, conversions)
- Hostname filters in GA and migration to GA4 are the most effective protections
Practical Examples
Ghost spam in Universal Analytics
A site owner discovers hundreds of sessions in Google Analytics referred by 'free-share-buttons.com' and 'success-seo.com'. Checking the hostname, they find these sessions never touched their site: it's ghost spam sent directly to their tracking ID.
Crawler referrer spam
A bot actually visits a website with a forged HTTP Referer header of 'best-seo-offer.com'. The site logs the visit in its server logs and Google Analytics. The owner visits the referring site and finds a dubious SEO tool sales page.
Google Analytics filtering
An administrator creates a GA filter to only include traffic with a valid hostname (their-domain.com). They also add a segment to exclude known spam referrers. Ghost traffic disappears from reports.
Frequently Asked Questions
Check the Acquisition > All Traffic > Referrals report. Signs of spam include: 100% or 0% bounce rate, 0-second session duration, unknown or suspicious domain names, and especially sessions with a hostname different from your domain (visible in Audience > Technology > Network > secondary dimension: Hostname).
GA4 is significantly more resistant to ghost spam because it uses a different data model and more robust authentication mechanisms (Measurement Protocol with API secret). However, crawler referrer spam remains possible. It's recommended to configure filters in GA4 and use a firewall like Cloudflare to block known bots.
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Last updated: 2026-02-07