When I boot my computer up, a balloon pops up saying something like (sorry - the balloon has now vanished) "You may have a Security problem. Click here to see."

When I click, I get Windows Security Center. Firewall and Automatic Updates are both marked on. Virus protection is marked check status. It goes on to say "Norton Antivirus reports that it is installed but its status is unknown." It goes on to invite me to click recommendations. One of them is make sure your anti-virus program is on...which I have done. It is on (Norton Anti-virus) and is up-to-date. System status is ok and every green box is ticked.

How can Windows Security Center be informed of the status of Norton anti-virus?

You don't say which Norton AV version you have (I use 2003) but one of the Norton updates a while back let the XP Security Centre know about the status of Norton AV. Are your Norton downloads through Liveupdate up-to-date?

Is your paid subscription up-to-date?

i_XpUser

Many thanks to you both.

Answer is: using Norton Antivirus 2003.

My paid subscription is up-to-date.

When I was invited to run Norton Antivirus Live Update a few moments ago and did so, the Security Center message changed to show that everything was OK - and there was also a message from Norton Antivirus to invite me not to receive "Redundant" Windows Security Center messages about the state of Norton Antivirus.

At the moment, I have rejected that invitation: because the Security Center stuff tells me about Windows Firewall and Windows XP updates which presumably Norton Anti-virus doesn't.