bbtang questions

• Is this code vulnerable to hacker attack?
• PHP string concatenation using ","?
• Track where users come from in PHP?
• Should I use php mail function or phpmailer?
• Is there a limit when using php mail function?
• Is this a proper way to destroy all session data in php?
• What do I need to store in the php session when user logged in?
• In MySQL, which collation should I choose?
• How to prevent code injection attacks in PHP?
• How to set initial value and auto increment in MySQL?

bbtang answers