The open source Pale Moon [palemoon.org] Browser's archive server suffered a data breach and infection.
From the Data breach post-mortem [palemoon.org]:
There has been a data breach on the archive server (archive.palemoon.org) where an attempt was made to sabotage our project by infecting all archived executables on the server with a trojan/virus dropper. This post-mortem report is posted to provide full transparency to our community as to what happened (as far can be gathered -- see below), which files were affected, what you can do to verify your downloads and what will be done to prevent such breaches in the future.
[...]A malicious party gained access to the at the time Windows-based archive server (archive.palemoon.org) which we've been renting from Frantech/BuyVM, and ran a script to selectively infect all archived Pale Moon .exe files stored on it (installers and portable self-extracting archives) with a variant of Win32/ClipBanker.DY (ESET designation). Running these infected executables will drop a trojan/backdoor on your system that would potentially allow further compromise to it.
The moment this was reported to me on 2019-07-09, I shut down access to the archive server to prevent any potential further spread of infected binaries and to start an investigation.
[...]Our data on this is limited, because in a later incident (likely by the same party or one other with similar access) on 2019-05-26 the archive server was rendered completely inoperable [palemoon.org] to the point of having widespread data corruption and being unable to boot or retrieve data from it. Unfortunately that also means that system logs providing exact details of the breach were lost at that time.
After becoming inoperable, I set up the archive server again on a different O.S. (moved from Windows to CentOS, and changed access from FTP to HTTP as a result considering Linux FTP can't be easily set up the same way and this server is purely a convenience service for users).
[...]This affected all archived executables (installers and portable exes) of Pale Moon 27.6.2 and below. Archived versions of Basilisk on the same storage server, although some would have already been present at that time, were not affected or targeted. Only files on the archive server were infected. This never affected any of the main distribution channels of Pale Moon, and considering archived versions would only be updated when the next release cycle would happen, at no time any current versions, no matter where they were retrieved from, would be infected.
Of note: only the .exe files on the server at the top level were affected. Files inside the archives (extract-able with 7-zip from the installers/portable versions or files inside the zip archives) were not modified.
If you never downloaded from archive.palemoon.org, you are almost certainly in the clear.
The post goes on to suggest that you verify your download by checking the code signing on the executables, where available, against .sig files provided, and/or against the SHA256 hashes provided.
It also notes:
Additionally, the infection is known to all major antivirus vendors and you can scan your downloads/system with your preferred mainstream antivirus scanner to verify the installers are clean.
Your humble editor has been using Pale Moon almost exclusively for four years, but has always practiced good download hygiene and always verified a download against the provided SHA256 hash. Also, since downloads were never from the archive server, it appears there was not even a potential to be affected in this case.
Out of an abundance of caution, Windows Defender was run and no infection of any kind was reported.