Advisories are messages that Windows Live OneCare sends to your computer to inform you of a new or changed security threat that you should know about. The content of an Advisory will vary depending on the type of threat. The Advisory might contain simple steps that you can take to guard against the threat, or a link to newly released security updates that you can install immediately.
No, Advisories do not expire because even though the issue that prompted the Advisory may have been addressed or mitigated by various updates to your computer, the issue may still be present on your computer, but inactive.
Advisories that are still active will remain on your Windows Live OneCare screen as an Action to Take. Depending on how many action items you have, you might have to scroll down to find the one you're looking for. To view the Advisory again, just click Recommendations. Inactive Advisories are also available at the Windows Live OneCare Advisories home page.