Website security starts with one rule from Mozilla that says never trust data from the browser. Sanitize all input and use parameterized queries to stop SQL injection. Encrypt traffic with HTTPS and HSTS and use strong passwords with two factor authentication. Apply updates after you backup and test them, then scan the site with a vulnerability scanner.
Your website stores customer data and a single weak form can expose it. Most attacks use a few well known flaws.
This guide lists the common threats and the defenses that Mozilla and OWASP document for site owners.
What is the First Rule of Website Security?
Mozilla states that you should never trust data from the browser. That includes URL parameters, POST bodies, HTTP headers, cookies and uploaded files. Sanitize all incoming data before you display it, use it in a database query or pass it to the operating system. See Mozilla website security guide.
What are the Common Website Threats?
| Threat | What it Does | Defense |
|---|---|---|
| Cross-site scripting | Injects scripts that steal session cookies in other browsers | Sanitize input and remove dangerous markup |
| SQL injection | Alters a database query to steal or delete data | Use parameterized queries |
| Cross-site request forgery | Triggers actions through a logged in browser | Require a secret token on every state changing request |
| Clickjacking | Overlays a hidden page to capture clicks | Set headers that stop framing |
| Denial of service | Floods the site with requests | Filter traffic before the web server |
How do You Stop SQL Injection?
Mozilla shows that joining user input into a query makes that input part of the query. Parameterized queries treat input as data only.
# Unsafe: input is joined into the query text
# statement = "SELECT * FROM users WHERE name = '" + user_name + "';"
# Safer: the driver passes input as data
cursor.execute("SELECT * FROM users WHERE name = ? AND password = ?", (name, password))Web frameworks apply many of these protections by default, so use their database tools and avoid raw queries.
What Other Security Steps Matter?
- HTTPS and HSTS. Mozilla advises encrypting traffic so credentials, cookies and form data remain private.
- Strong passwords. Encourage them and consider two factor authentication.
- Software updates. Apply security patches. Backup data first and test updates before you deploy.
- Vulnerability scanners. Use automated security testing against your site.
- Less stored data. Store and display only what you need, for example the last four digits of a card number.
What is the OWASP Top 10?
OWASP describes its Top 10 as a standard awareness document for developers and web application security. Its most current release is the 2025 edition. Mozilla advises that you track it and address the most common flaws first. See the OWASP Top 10 project.
For business wide measures see online security measures for your business. For cloud hosted sites see the top security issues in cloud computing.
Frequently Asked Questions
How do I Secure My Website?
Sanitize all input, use parameterized queries, encrypt traffic with HTTPS and HSTS and apply updates after you backup and test them.
What is SQL Injection?
It is an attack where user input alters the meaning of a database query. Parameterized queries stop it.
Does HTTPS Make a Website Secure?
No. HTTPS protects traffic in transit. You still need input handling, updates and strong passwords.
What is the OWASP Top 10?
OWASP describes it as a standard awareness document for web application security. Its 2025 edition is the most current.
When should I Update My Site?
Apply security patches as soon as you can test them. Mozilla advises a backup and a test before you deploy.
Key Takeaways
- Never trust data from the browser.
- Parameterized queries stop SQL injection.
- HTTPS and HSTS protect traffic in transit.
- Updates need a backup and a test before deployment.
- OWASP Top 10 lists the flaws to address first.
Sources and References
This guide follows Mozilla and OWASP documentation.
- Website Security (MDN Web Docs) developer.mozilla.org
- OWASP Top 10 (OWASP) owasp.org