For Users with CA Antivirus installed on their machine - this post will be a big sigh of relief.
SVCHOST.exe and CA Antivirus software have been lately fighting with each other for CPU and memory resources. CA has confirmed this problem and will return with a fix soon.
Till then temporary solution to your slow computer and SVCHOST hogging 50% of your CPU is:
Disable CA Antivirus Realtime protection
OR
Disable Automatic Updates
OR
Exclude CA Antivirus to scan *.msi and *.msp files.
The above will definitely solve your SVCHOST.exe and Automatic updates problem