A security platform may determine, during receipt of a file, metadata associated with the file. The file may be intended for a client device. The security platform may compute, based on the metadata and during the receipt of the file, a hash associated with the file. The security platform may identify, during the receipt of the file, a stored hash that matches the hash associated with the file. The security platform may determine a security classification of the file based on information associated with a security classification corresponding to the stored hash. The security classification of the file may be determined before the receipt of the file is complete. The security platform may selectively permit, based on the security classification of the file, the client device to complete a receipt of the file.