This is a background process that runs as a host for other programs/processes. Often you can see more than one instance of svchost running at the same time in Task Manager, (right click the Task Bar, select Task Manager, then the Processes tab), so it is may be that the problem is not with svchost.exe itself, (otherwise other processes could not use it), but with a particular process. In your case it would appear to be a networking process of some sort.
However, there are viruses that pretend to be svchost and you should really be prepared to revisit your antivirus software, update its definitions, and rescan. Also, you need anti-spyware applications to check for spyware. Have a look at this site;
click the S, and scroll way down to svchost, and see what is said about svchost and the virus variants.
Having said all that, as Event Viewer shows up svchost having problems with "ntdll.dll", I did some research on ntdll.dll. Ntdll.dll is an NT layer DLL file that controls Windows NT system functions. No, I don't know what tht implies, but at Experts Exchange I found a discussion about a problem similar to yours. The discussion thread is here;
At first glance it would seem that you have to sign up to Experts Exchange to see the solution, but that is not the case. Simply scroll down the page, and the discussion starts. Beware though, this particular discussion is very long and involved, and is not easy to follow. Many suggestions are offered, and some work whilst others do not.