A client sends a file information request to a security server, where the file information request identifies a URL from which the client is attempting to download a file. Upon receiving the request, the security server determines the stability information of the identified URL and provides the requested file information for the file provided by the URL. The security server determines the stability information of a URL by analyzing the file identifiers and URLs identified in downloaded file reports received from multiple clients. The determination of the stability information of a URL may be based on a variety of factors, such as stability of a URL over time, a textual analysis of the URL, and the set of files provided by the URL. A user of the client can review the file information and decide whether to expend the resources to download the file.