Collaborative filtering recommenders are highly vulnerable to malicious attacks designed to affect predicted ratings. Previous work related to detecting such attacks has focused on detecting profiles. Approaches based on profile classification to a large extent depend on profiles conforming to known attack models. In this paper we examine approaches for detecting suspicious rating trends based on statistical anomaly detection. We empirically show these techniques can be highly successful at detecting items under attack and time intervals when an attack occurred. In addition we explore the effects of rating distribution on detection performance and show that this varies based on distribution characteristics when these techniques are used.