How to Stop Fake Signups on Your SaaS Product

Fake signups are more than a nuisance — they quietly drain your resources, distort your metrics, and open the door to abuse.

If you’re running a SaaS business and offer a free trial or freemium plan, chances are you’ve already seen this:

• Accounts with gibberish names
• Temporary email addresses
• VPN or proxy IPs
• Signups that never log in again

We’ve been there. At OnSefy, we saw it firsthand — and built a solution to fight back.

In this post, you’ll learn:

• Why fake signups happen
• What damage they do
• How to detect and block them
• Tools and techniques to protect your platform

Why Are You Getting Fake Signups?

Fake signups come from various bad actors:

• Bots scanning your site for vulnerabilities
• Abusers trying to exploit free trials, referrals, or credits
• Competitors scraping or reverse-engineering your app
• Click farms testing automation tools

They use:

• Disposable emails (Mailinator, Temp-Mail, etc.)
• Headless browsers or automated scripts
• Fake names generated by AI
• IP obfuscation via proxies or VPNs

The Real Cost of Fake Signups

Many founders ignore fake signups early on, but the damage adds up fast.

💸 Operational Costs:

• Email/SMS verifications sent to invalid accounts
• Cloud storage, API, or compute resources wasted
• Support team chasing down bugs from noisy data

📉 Product Impact:

• Analytics skewed by fake activity
• Funnels polluted with junk data
• Trials or onboarding systems abused

🤖 Abuse Risk:

• Referral fraud or affiliate manipulation
• Potential phishing/spam using your brand
• Higher chance of being flagged as a spam domain

Every fake user takes value away from your real ones.

How to Detect Fake Signups

Here are 5 early signals that indicate fraudulent signups:

1. Email Domain

   • Temporary or known fake domains
   • Misspelled brand names (e.g., gmaill.com)

2. IP Address

   • Proxy, VPN, or data center IP ranges
   • Country doesn’t match email TLD or timezone

3. Name & User Agent

   • AI-generated names etc
   • Same browser/device across many signups

4. Timing Patterns

   • Multiple signups in seconds from one IP
   • Odd hours or rapid navigation

5. No Further Engagement

   • No login after registration
   • High bounce rate from welcome email

How to Block Fake Signups (Without Killing UX)

Here’s a practical anti-fraud stack that balances security and usability:

✅ 1. Validate Email Domains

• Block disposable domains
• Maintain a blacklist or use an API to auto-validate emails in real time

✅ 2. Rate-Limit Signup Attempts

• Throttle based on IP, user agent, or device fingerprint
• Prevent brute-force or mass form submissions

✅ 3. Use Smart CAPTCHAs

• Show CAPTCHA after form validation, not before
• Use invisible reCAPTCHA or hCaptcha for low-friction protection

✅ 4. Fingerprint Clients (with consent)

• Track browser/device traits (resolution, OS, timezone)
• Identify suspicious duplicates or automation patterns

✅ 5. Use a Fraud Detection API like OnSefy

Tools like OnSefy give you real-time scoring based on:

• IP reputation
• Email domain trust
• Device/browser behavior
• Pattern recognition across user data

You get a risk score and risk level you can use to:

• Automatically block high-risk signups
• Flag suspicious accounts for review
• Maintain clean onboarding funnels

Why We Built OnSefy

As SaaS founders ourselves, we were wasting time on fake users, broken onboarding, and bad data. So we built OnSefy — a developer-friendly fraud prevention API focused on real-time signup validation.

It works with:

• Just one API call during signup
• No cookies or tracking scripts
• Fast, accurate, and privacy-friendly

👉 Try the free plan at OnSefy.com

Conclusion: Fake Signups Cost You. Stop Them Before They Start.

Whether you’re a solo indie hacker or running a scaled SaaS, fake signups are a real problem. The earlier you address them, the more time and money you’ll save.

Don’t wait until your metrics are a mess or your system gets abused.

✅ Start with email validation and smart rate limits ✅ Add behavioral monitoring and CAPTCHA ✅ Use tools like OnSefy to block fraud before it enters your database

If you need help integrating signup protection into your stack, get in touch — we’d love to help.