1. The document presents a system to filter unwanted messages from user walls in online social networks. It aims to give users more control over the content that appears on their walls. 2. A machine learning classifier is used to automatically label messages by category. Users can then specify filtering rules to block certain categories or keywords from appearing. 3. The system also implements a blacklist to temporarily or permanently block users who frequently post unwanted content, as determined by filtering rules and a threshold.