With the boom of social media, it has become increasingly easier for ordinary people to not only post their own content but share other people's content on the Internet. In this paper, we conceptualize a growing problem of moving user data - once a user posts some content on the Internet, the data is largely out of her control; the content can be forwarded to or shared with other people, applications or websites, potentially causing various privacy issues. We present a technical solution that aims to provide users flexible fine-grained control over their moving data. Our system builds upon the ideas of data envelope with sticky policy, reactive access control, and privacy scores. Users can specify and enforce sticky policies of their data through our data envelope plug-ins. Our reactive access control mechanism allows users to grant access to their data on the fly, extending the pre-defined sticky policies to better fit with the dynamic nature of people's sharing practices. Finally, the privacy score helps users make decisions about data requests by providing relevant privacy risk assessment information about the requesters.