svchost.exe memory usage up to 4Gb every hour, how to fix?

Process Explorer will tell you which services are running in a given svchost.exe process. You can use that information to narrow down the range of services that you need to start/stop to see what is using all of your memory.

In addition to Process Explorer, in Task Manager in Windows 7 you can right click on any of the processes and click "Go To Service(s). This will highlight which services are being run by this process.

It could be a sign of malware, see my post here

Use the "Alternate Method"

Read the "EDIT" section also.