Can hacker hack session_data?

[eluser]Unknown[/eluser]
[quote author="WanWizard" date="1340780038"]If your session data is in the database, if a hacker can access that they can access all data, so I shouldn't worry about sessions in particular.

Use proper validation, XSS filtering and CI's DB layer to protect yourself against SQL injection attacks, which are the best way to get into your database.[/quote]

so i am entirely secure from malicious users that modify sessions if my session data is in the database?

i have read from many articles that codeigniter's xss filtering is not secure. is there other xss filtering libraries that i can put into my application?