Recently I was testing an Adware bundle and ran across a new Tech Support Scam that I had not previously seen before. There was nothing remarkable about this scam as it just downloaded an image of a fake Windows error that tells the victim to call 1-844-324-6233 for assistance, and then displayed it over all the other active Windows to make it difficult to remove.

It wasn't until I looked at its source code that I saw that this tech support scam also gave the malware developers the ability to remotely execute commands they wanted on the infected computer.

WinCPU Lock Screen
WinCPU Lock Screen

The main component of this Tech Support Scam is a file called WinCPU.exe. As the program is created using .NET, we have the ability to decompile it and see exactly how it works. What I found was very disturbing and is the first time I have seen a Tech Support Scam Trojan bundling a backdoor inside it.

The source code below shows that on startup, the WinCPU program will connect to a remote Command & Control server and receive a command to execute.

WinCPU.exe Source Code
WinCPU.exe Source Code Snippet

It does this by connecting to the site and sending the MAC address of the computer. An example request can be seen below:

In response, the Command & Control server will reply with a command that WinCPU will then execute on the infected computer. This command will be in the format command:::[command to execute here].

Communicating with the C2
Communicating with the C2

For example, if the malware developers wanted to open a particular web page every 5 minutes, they could issue the command:


Thankfully, their current implementation contains some weakness that makes it a bit difficult to execute more intricate commands, but this is trivial to fix. 

WinCPU.exe will then connect every 5 minutes to the Command & Control server for new commands to execute. 

This type of backdoor or remote access behavior is expected with malware, but not with programs being distributed via Adware bundles. As I have repeatedly said in the past, Adware and potentially unwanted programs are becoming a serious problem. These adware purveyors are earning a lot of revenue from these types of programs and until the FTC or other government agency does something about it, it will just continue.


Files associated with the WinCPU Tech Support Scam:

C:\Users\Default\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\ClientProtocol\wincpu.exe

Registry entries associated with the WinCPU Tech Support Scam:

HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Run\wincpu	C:\Users\Default\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\ClientProtocol\wincpu.exe

Network Communications:


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