In the world of Technical SEO, we spend a lot of time worrying about crawl budgets and schema markup. But there is a silent killer of SEO equity that often goes overlooked by marketing teams: Subdomain Hijacking.
What is Subdomain Hijacking?
Subdomain hijacking (also known as subdomain takeover) happens when a subdomain points to an external service (like GitHub, Heroku, or an old Shopify store) that has been deactivated, but the DNS CNAME record remains active.
"An orphaned DNS record is an open invitation for malicious actors to claim your brand's authority for their own gain."
The SEO Risk
Because subdomains often inherit some authority from the root domain, a hijacked subdomain can rank for high-competition keywords while hosting malicious content, phishing sites, or spam. To Google, this looks like your brand is suddenly hosting high-risk content.
How to Audit for Takeovers
As SEOs, we should be auditing our DNS records as part of our quarterly technical health checks. You are looking for 404 or No Such Bucket errors on subdomains.
# Example check for orphaned CNAMEs
dig dev.yourwebsite.com CNAME
# If the response points to a service you no longer use: Fix it!Key Takeaways
- Audit your DNS: Use tools like Screaming Frog to crawl your subdomains and check for status codes.
- Close the Loop: When you delete a landing page platform or staging site, delete the DNS record immediately.
- Monitor Search Console: Keep an eye on the "Security Issues" report.
Web security isn't just a job for the DevOps team. It's an integral part of maintaining the integrity of your technical search strategy.