Rules of Programming: Always Validate Input Data!
This one is often forgotten, yet it's one of the most important and fundamental corner stones in programming.
Validating (user) input data is a must. Always assume the input you deal with can make bad things.
What you should think of:
- Character encoding
- Encoding and validating HTML data
- Verifying e-mail addresses and passwords
- Security risks like Cross-site scripting
Code for bad input first - good input last. You'll help yourself!
Rule #17 of programming:
Always validate input data!