1. A method for restricting access to electronic data in a file, the method comprising: determining, by a computing device, a remote header identifier for the file, the remote header identifier comprising a pointer or link to a remote header that is maintained at a server machine remote from the file and containing at least a portion of security information related to the file; encrypting, by the computing device, the electronic data using a file key; encrypting, by the computing device, the file key using a public key associated with the remote header identifier to form an encrypted file key, wherein the encrypted file key is needed to decrypt the electronic data; forming, by the computing device, a secured file, the secured file including: a header portion, including at least the remote header identifier and the encrypted file key; and a data portion, including at least the encrypted electronic data; and retaining the secured file in place of the file; wherein the security information comprises a private key corresponding to the public key and access rules indicating one or more user groups entitled to access the file and at least one of a location or a time the one or more user groups are entitled to access the file, and wherein the private key is used to decrypt the encrypted file key, and wherein the server machine is configured to alter the security information in the remote header without changing the secured file.