I am using MS XP Pro, SP2. All Windows updates have been applied. I am using Norton AV 2005 and Zonealarm Pro. Again all updates have been applied. I have made no changes to the compter for a number of weeks and lately (in the last 2 weeks) I have been getting the "Revocation information for the secuity certificate for this site is not available. Do you want to proceed?" window popping up when I visit sites such as PayPal. I do not get the message every time I visit a secure website and I have received the message visiting both secure and non-secure websites.
The privacy control in Zonealarm is set to high for banner control and medium for cookie control. The secuity setting in MSIE is set to high for restricted sites, medium for the Internet.
I have run Ad-Aware, Spybot and XoftSpy to check for trojans and have found none.
Any ideas on what may be causing this to suddenly do this?