mikkel wrote:
svchost.exe is a host platform for NT services. Active applications don't affect the number of svchost.exe instances open, but running services do. Multiple services can be hosted in one instance, which is done for most native Windows services. You see multiple svchost.exe instances running on a fresh install, as each instance hosts services with different user privileges. Over time, you may encounter several instances of svchost.exe operating under the same user privileges, for various reasons.
Pop open a command prompt and put in "tasklist /SVC", and you can see which services are hosted in the svchost.exe instances that are leeching your system memory.
^ the correct answer ^
also, if a gui suits your needs better than the command prompt, download
process explorer. it will give you a real-time look at all the running processes on your system, including those that are running within the svchost process. you can then see if possibly a spyware/viral process is running as a system service. good luck!