What potential issues can arise when using an outdated PHP login script after a server PHP version update?

When using an outdated PHP login script after a server PHP version update, potential issues can arise due to deprecated functions or syntax that may no longer be supported in the updated PHP version. To solve this issue, you should update the login script to use current PHP best practices and functions to ensure compatibility with the new PHP version.

// Example of updating an outdated PHP login script

// Old code using deprecated functions
$hashed_password = md5($password);

// Updated code using password_hash() function
$hashed_password = password_hash($password, PASSWORD_DEFAULT);