When checking for updates, it stops and says error found: code 0x80072f78. i am running vista premium on a sony vaio laptop. any help please

windows defender is a joke, install your own antispyware like spybot or avg antivirus

Well, Vista is well known for being sucky, for lack of a better word, as is windows defender. But if you search your error code on google, you'll get thousands of hits with people having problems just like you, just follow what they were told to do. For example, you might try this: http://forums11.itrc.hp.com/service/forums/questionanswer.do?admit=109447626+1215635501330+28 353475&threadId=949462

You already diagnosed the problem: You're running Vista. Here's a little advice which may help: Disable Windows Defender, Windows Firewall, and UAC, and get 3rd party software like Kaspersky (if it will let you install it). Or buy a copy of XP and downgrade. Or get openSUSE 11.0 KDE 4.0 with Compiz Fusion for free; it will remind you about Vista in terms of looks and it won't give you error messages.

I would uninstall windows defender, it's not that great of a program and install spybot, which works a lot better. I used to use defender, but got rid of it and installed spybot.