Are you using Internet Explorer? If so, go to Internet Options (in the Tools group) and click on Advanced. Scroll down to Security and make sure the choice "Empty Temporary Internet Files folder when browser is closed" is unchecked. If it's been checked, your Mudcat cookie is being thrown out every time you close your browser. If you uncheck it and find it's been checked again when you run your virus checker, you may want to look at the settings for the virus checker.