What is referrer spam?
Referrer spam is fake traffic sent with a forged referrer header so that the spammer's domain appears in your referral report and tempts you to visit it. Some variants never touch your site at all, hitting the analytics endpoint directly. It inflates sessions, distorts bounce rate, and pollutes every source report.
Worked example
A small site's referral report before filtering.
| Total sessions reported | 3,410 |
|---|---|
| Sessions from three unfamiliar .xyz domains | 820 |
| Bounce rate on those sessions | 100% |
| Engagement time on those sessions | 0 seconds |
| Sessions after filtering | 2,590 |
24% of reported traffic was spam It is not only the session count that was wrong. Site-wide bounce rate, average engagement time and every conversion rate denominator were being computed over a quarter of traffic that never existed.
Two kinds, one symptom
Crawler spam is a bot that genuinely requests your pages with a forged Referer header. It consumes real bandwidth, it appears in your server logs, and any analytics that runs server side or fails to classify bots will record it.
Ghost spam never visits your site. The spammer sends fabricated hits straight to the analytics collection endpoint, guessing or scraping the site identifier. Nothing appears in your server logs, which is the giveaway: traffic that exists in analytics and nowhere else.
Ghost spam was rampant in tools whose collection endpoint accepted any site id from anywhere without validating the origin. Endpoints that validate the sending domain are considerably harder to poison.
How to recognise it
100% bounce rate, zero engagement
Spam sessions never interact. A referrer whose sessions are all one page and zero seconds is not a real audience.
A domain that makes no sense
SEO service pitches, adult sites, crypto offers and freshly registered domains on cheap TLDs. Nobody linked to you from those.
Traffic that is missing from server logs
The definitive test for ghost spam. If the visit is in analytics but not in your access logs, it never happened.
An impossible geographic or hostname pattern
Sudden traffic from one country you do not serve, or hits reporting a hostname that is not your site, both point at forged data.
Live demo
See it on real data. The live demo is a fully populated dashboard on demo traffic, with no signup and no card.
Open the live demoWhy it matters more than the session count
The obvious damage is inflated traffic. The expensive damage is downstream, because spam sessions land in the denominator of everything.
- Bounce rate rises, because spam sessions are always single-page.
- Average engagement time falls, because they contribute zero seconds each.
- Conversion rate falls, because they never convert but do count as opportunities.
- Channel reports mislead, because referral looks larger than it is.
A site with 24% spam is making budget decisions against a conversion rate that is understated by roughly a quarter. That is the real cost.
How mrkr filters it
mrkr classifies referrers at ingest against a maintained list of known referrer-spam and low-quality domains, and drops those hits rather than counting them and hoping you notice. Bot and crawler user agents are classified in the same pass.
The scale of what gets removed is easy to underestimate. Measured over 30 days on a live site running mrkr, 12,146 bot hits were filtered against 2,946 human pageviews, which is 4.1 times the human traffic.
Filtering at ingest rather than in the dashboard matters, because a filter applied at read time still leaves the spam in every historical aggregate and in every exported report.
FAQ
How do I stop referrer spam?
Use analytics that filters known spam domains and bot user agents at ingest rather than expecting you to add exclusion rules yourself. Server-side blocking helps against crawler spam, but ghost spam never reaches your server, so it can only be handled at the analytics endpoint.
Does referrer spam hurt my SEO?
Not directly. The links are usually fabricated in a header rather than published anywhere, so there is nothing for a search engine to see. The damage is to your own decision-making, because it corrupts every rate metric you report.
How can I tell ghost spam from a real referral?
Check your server access logs. Real traffic appears in both the logs and analytics; ghost spam appears only in analytics because it never requested a page. A referrer with 100% bounce rate and zero engagement time is the other reliable tell.
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