Newly come here I must admit the demos and features of SilverStripe look great to me.
Before using SS on a production website I'd like to now how secure it is against hacking... is there, for instance, any systematic vulnerability check conducted... or any forum thread gathering exploits and patches... I found none of those.
The most common security error I have come across is people not changing the default admin/password. Also running the site in 'Live' mode rather then 'Dev' mode on servers is also recommended as Dev mode will output error logs which may contain your DB details as I found out. If you have any recommendations or come across anything you think could be exploited feel free to let us know!
Stating the the security of any bit of software is flawless is just inviting trouble, so I'm not going to claim that, however I can say that to date there have been no known security breaches of SilverStripe sites (and SilverStripe has been deployed on a range of very high profile sites).
There have been a few minor security related bugs which have been discovered over the past 18 or so months, which have all be resolved promptly and (to my knowledge) have never been exploited.