Hi,
The temp files are not virus related. These temp files are generated by the web service’s xml serialization. In oder to know why the temp xxx.dll file writing failed, you should check event viewer. Generally you will see some specific events after you reproduced the issue. There should be some detailed information in the event content that can help us address the root cause.
Since sites will work properly after killing w3wp.exe which is consuming the most memory, I’ d suggest enabling the Memory Recycling feature of your website’s application pool. This should help you temporarily work around the problem.
On the Recycling tab of your application pool's properties dialog box, you can specify the value of the Maximum virtual memory and Maximum used memory(“Physical memory is commonly used for ASP.NET applications because of the way the common language runtime's garbage collector works, Virtual memory is commonly used for classic native applications that fragment the heap”). If the worker process exceeds this Maximum value, a new process is created to replace it, and all current requests are reassigned to the new process.