There’s an excellent thread going on over at stackoverflow.com about suggestions for what every programmer should know about security.

Some of the more interesting highlights:

• Never trust user input!
• Validate input from all untrusted sources - use whitelists not blacklists
• Plan for security from the start - it's not something you can bolt on at the end
• Keep it simple - complexity increases the likelihood of security holes
• Keep your attack surface to a minimum
• Make sure you fail securely
• Use defence in depth
• Adhere to the principle of least privilege
• Use threat modelling
• Compartmentalize - so your system is not all or nothing
• Hiding secrets is hard - and secrets hidden in code won't stay secret for long
• Don't write your own crypto
• Using crypto doesn't mean you're secure (attackers will look for a weaker link)
• Be aware of buffer overflows and how to protect against them

There are some excellent books and articles online about making your applications secure:

• Writing Secure Code 2nd Edition - I think every programmer should read this
• Building Secure Software: How to Avoid Security Problems the Right Way
• Secure Programming Cookbook
• Exploiting Software
• Security Engineering - an excellent read
• Secure Programming for Linux and Unix HOWTO

Check out the full discussion here: What should every programmer know about security? (via stackoverflow.com)