Abstract Collaborative recommender systems are vulnerable to malicious users
who seek to bias their output, causing them to recommend (or not recommend)
particular items. This problem has been an active research topic since 2002. Researchers have found that the most widely-studied memory-based algorithms have
significant vulnerabilities to attacks that can be fairly easily mounted. This chapter
discusses these findings and the responses that have been investigated, especially
detection of attack profiles and the implementation of robust recommendation algorithms.