Windows Defender launches at login

For the past 3 or 4 days, when I log in to Vista (Ultimate x64), Windows
Defender has been launching during startup. It indicates no problems, and
there have been no recent changes. I don't see any recent updates that
appear to be related.

Is this a recent change, or has my Defender developed a glitch? I have
checked for malware and see no evidence of any.

Any ideas?

Hi Duc,

It may have a Quarantined item that it wants you to look at. Open Windows Defender, Click Tools, Click Quarantined items. Apply the actions you want to anything listed.

Hope this helps,
Shawn