Hardware, software, and network problems; human error; and malicious attacks can all cause degredation of pages you have archived. Hardware can malfunction and disks crash. Software can be affected by bugs, viruses, or misuse. Errors can occur as data transmitted from one computer to another. Humans can cause fail to catch mistakes they make. Files can be corrupted by malicious hackers. To assure content integrity you should create and follow a policy for regular maintenance. This entails checking new files as they are added and regularly checking old ones. For checking files, there are tools, including no-cost, open source tools, that help automate the process.