What is this White Rectangle on Windows Desktop?

When I started my Windows PC this morning there was a small white rectangle that appeared on the screen. It first appeared near the bottom left corner of the desktop, but I could drag it anywhere on the PC screen. Because it could be dragged I knew it is a hidden window for some application being run on my computer. But which application does it belong to, I had no idea. The first thing that came to my mind is that finally some slick malware slipped under the radar of the installed protection ESET Internet Security.

If you have also encountered something similar and are becoming suspicious whether your computer is infected by malware then there are some steps to find out very easily.

Investigating Suspicious Window

Here are the steps to find out which application this small window belongs to:

  1. Download Process Explorer from https://learn.microsoft.com/en-us/sysinternals/downloads/process-explorer. Extract the contents of the downloaded ZIP file, right-click  on procexp64.exe and choose Run as Administrator from there.
  2. In the Process Explorer window, click on the cross-hair icon, hold and drag it over the window in question. In our case, we drag it over the small white rectangle window.Investigating Suspicious Window
  3. As soon you drop this icon over the window under investigation, Process Explorer finds the process associated with that window and highlights it in the list of processes. In my case, it turned out to be the ESET Online Scanner that I had used a few months ago and had forgotten all about it.Investigating Suspicious Window

In this case, it turned out to be just another security product that I had used a few months ago. This was a relief and I ended up removing it because I had installed a regular antivirus (ESET Internet Security) after that. But if you are investigating a window and it does not look familiar, then you can right-click on it in Process Explorer and choose Check VirusTotal to see if it is flagged as malicious by VirusTotal which is powered by more than 40 different antivirus engines.