Today, I just have a short public service announcement: You MUST run an adblocker while using Google. It may be best just to keep the adblocker enabled all the time.

Ads have been important in supporting many good (and, of course, bad) content on the web. It has been a long standing "social contract" to allow ads to help support creators of valuable content. But sadly, ad networks have not provided any due diligence verification of the ad buys they accept. As a result, in particular, ads displayed as part of Google search results are often used to distribute malicious software impersonating popular products. Open-source and free products are particularly vulnerable. They usually cannot pay for competing for ads to reduce the effectiveness of malicious advertisements. 

Image via Twitter (Will Dormann @wdormann)

Recently, Malwarehunterteam [2] has done a great job to alert of malicious ads via Twitter, and they do have some create recent examples:

• A malicious ad impersonated OBS Studio. 
• Just searching for the keyword "VirtualBox" lead to malware.
• Searching for VLC led to malware.

Aside from "not clicking on ads," how do you protect yourself? It is often not easy to distinguish malicious from non-malicious links. Many malicious sites use plausible domain names. Here are some tips:

• Run any binary you download through Virustotal. Interestingly, Virustotal is owned by Google but Google does not appear to take advantage of Virustotal to block malicious downloads.
• Verify digital signatures (but hashes and signatures posted on the same site as the download may be fake as well)
• Dig a bit deeper into the website you download the software from. Is it "complete" or just a download page?
• If you usually have to pay for software, but a website offers it for free: It is likely malicious.
• Do not trust the link displayed in Google ads. Verify the URL you download the software from.

All these steps help but are not perfect. Due to the scale of this problem, a recent FBI advisory also recommended using adblockers. 

[1] https://twitter.com/wdormann/status/1614675821578395655
[2] https://twitter.com/malwrhunterteam
[3] https://www.ic3.gov/Media/Y2022/PSA221221?=8324278624

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Johannes B. Ullrich, Ph.D. , Dean of Research, SANS.edu
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