Recent attempts to update have failed (Vista) and their troubleshooting guide has been no help. Have recently installed Bit Defender which seems to coincide with this problem and am wondering if Bit Defender is preventing the updates although that seems strange. I am also getting a Bit Defender message svchost.exe is regarded as a threat and terminated. This happens several times in a session. Any ideas folks?
Try turning off “real-time-protection” in Bit Defender whilst updating Windows and turn it back on when you’ve updated.
I don’t use Bit Defender myself but have seen this problem mentioned in other forums and the above solution seems to work for most people.
I’m not sure about svchost.exe but I believe it’s a Windows communication process that can be run by several programs.
I would suggest that as a precaution you should make sure your virus definitions are up-to date and do a full virus scan and also download and run the free version of SuperAntiSpyware.
Better safe than sorry 
If for any reason you don’t want to use SuperAntiSpyware you could use Malwarebytes free version but it’s not as good as SuperAntiSpyware in my opinion.
Good luck
svchost is benign. if you have a look here it will explain more. http://www.howtogeek.com/howto/windows-vista/what-is-svchostexe-and-why-is-it-running/ a little out of date but try this too.
Tried turning off real time protection (that was BitDefender suggestion too) didn’t help. Have decided to bin it and have managed to install updates with it removed. I find it shocking that what is apparently quite a long standing issue has not been resolved. It’s been a bit of a pain from the start with this lot and customer service didn’t exactly shine so I’ll be glad to see the back of it.
Wouldn’t bother with any of the paid for AV type stuff unless it came with a new machine. Microsoft Security Essentials is all you really need these days.
http://www.microsoft.com/en-gb/security_essentials/default.aspx <= Link to Microsoft Download Centre.
As for Firewalls a software one is better than nothing but as most folks have a WiFi router given to them by their ISP the hardware firewall in that is much better just remember to change the default setting’s then it is about as much use as trying to stop your truck with a wet paper bag.