The use of fake software updates to spread malware is nothing new, but a new malware campaign has been detected that is somewhat different. Fake Adobe Flash updates are being pushed that actually do update the user’s Flash version, albeit with an unwanted addition of the XMRig cryptocurrency miner on the side.

The campaign uses pop-up notifications that are an exact replica of the genuine notifications used by Adobe, advising the user that their Flash version needs to be updated. Clicking on the install button, as with the genuine notifications, will update users’ Flash to the latest version. However, in the background, the XMRig cryptocurrency miner is also downloaded and installed. One installed, XMRig will run silently in the background, unbeknown to the user.

The campaign was detected by security researchers at Palo Alto Network’s Unit 42 team. The researchers identified several Windows executable files that started with AdobeFlashPlayer that were hosted on cloud servers not controlled by Adobe.

An analysis of network traffic during the infection process revealed most of the traffic was linked to updating Adobe Flash from an Adobe controlled domain, but that soon changed to traffic through a domain associated with installers known to push cryptocurrency miners. Traffic was later identified over TCP port 14444 that was associated with the XMRig cryptocurrency miner.

Further analysis of the campaign revealed it has been running since mid-August, with activity increasing significantly in September when the fake Adobe Flash updates started to be distributed more heavily.

End users are unlikely to detect the downloading and installation of the XMRig cryptocurrency miner, but there is likely to be a noticeable slowdown in the speed of their computer. The installation of the XMRig cryptocurrency miner may be stealthy, but when it runs it uses almost all of the computer’s CPU for cryptocurrency mining. Any user that checks Task Manager will see Explorer.exe hogging their CPU. As with most cryptocurrency miners, XMRig mines Monero. What is not currently known is which websites are distributing the fake Adobe Flash updates, or how traffic is being generated to those sites.

Any notification about a software update that pops up while browsing the internet should be treated as suspicious. The window should be closed, and the official website of that software provider should be visited to determine if an update is necessary. Software updates should only ever be downloaded from official websites, in the case of Adobe Flash, that is Adobe.com.

The Palo Alto researchers note “Organizations with decent web filtering and educated users have a much lower risk of infection by these fake updates.”