|Changing you Internet user name or password will generally have no effect on Internet access by any application, and that includes anti-virus utilities. The exception would be if you access the Internet with a proxy server and most home users do not.|
Applications access Internet services that have been made available by the system. They have no knowledge of such details as account names or passwords, unless of course a proxy server is being used.
If you are using an email service provided by your ISP you will need to update account details in your email client.