WannaCry was able to successfully run on ReactOS in 2025. Most other virsuses do tend to crash, because the memory layout is just a tiny bit different, but yeah, compatibility means compatibility. Lots of malware comes along for the ride.
However, there is a permissions layer that is more nix than Windows, which means the first foothold is still better than XP - you have to choose to execute the file. Self-running things don't tend to infect systems.
Its not a panacea, and there is a risk factor. And there aren't a lot of antivirus systems that can run correctly under ReactOS, because they freak out and think the OS is the malware, because they're scanning hashes for Windows, not another system.
But for a hobby OS, keeping hardware and software accessible after the rest of the world broke access, it still works.
Of course. Maybe not successfully but a "virus" is just software. If it runs software, it runs software, full stop. Maybe the same APIs are not available or behave differently, so it may be buggy or non-functional, but that's true of Half-Life here too.
Somewhere in the docs they state that they must also recreate whatever bugs the API has, otherwise applications written with those bugs as an (implicit) assumption could misbehave.
its worse than that, Windows activates/deactivates "bugs" based on the compatibility profile of the app.
so you can set an app to use a Windows XP compatibility profile, and this will simulate Windows bugs which were fixed in more recent versions of the OS
Maybe worry about Linux malware which is a major problem right now everyone is in huge denial about, instead of throwing shade at a hobby OS emulating a 25 year old version of Windows.
ReactOS isn't the one that just had one of its package repos owned (again).
I would still note that this is not some kind of unique problem to Linux. There have been documented instances of malware making it to the Play Store, which is supposed to have a much more rigorous vetting process than AUR and costs actual money to publish on.
Just to expand... When the above user is comparing to Windows, who got most of the US government breached, I do think shade against AUR is uncalled for. Its just a community host for packages, comes with warnings, and isn't enabled by default, etc.
I can still happily upgrade via pacman without fear. Haven't been able to update on Windows without concern for over a decade - the malware comes builtin.
I only have 4 packages installed with AUR and I think that’s the intention. You’re only going there when the other solutions aren’t available or don’t make sense.
Linux users used to say "Linux is secure and doesn't get viruses". Now the best thing we can say about it is "Linux gets viruses just like the Play Store". Sad if you ask me.
I think anyone who has made that claim was probably trying to be smug or didn’t actually understand security concepts, and was never correct to be making that claim.
Only Apple has made that claim in their marketing and that was 20 years ago when security by obscurity was shielding them, and when Windows XP was such a cesspool that anything with a normal amount of malware would look virus-free by comparison.
Isn't it funny how such incidents on Linux are rare enough that they make headlines, but on Windows that's been the baseline expected state of things for so long that nobody bats an eye anymore.
Btw if you're running an OS that's never had a malware incident, please, tell us!
...is essentially impossible to pull off against commercial operating systems, because their core components are all written in-house by staff with photo ID badges, details with HR, tax returns filed with the government, and a cubicle that makes sure that they're locals and not some faceless anonymous hacker identifiable by nothing other than a throwaway faked email address!
I get that there was a lot of "stigma" about open source, the world largely forgot about it, but... actually, in this sense of allowing anonymous contributions it remains a very real risk.
"Jia Tan" was almost certainly a paid professional hacker working for a nation-state actor. Their "helpful contributions" to XZ utils was nowhere near a full-time effort. They certainly had "other irons on the fire", most probably in the Linux kernel or immediately adjacent to it.
He's probably not the only one doing this kind of "work".
For all you know, Linux has more remote exploits purposefully baked into it than Windows has security bugs inadvertently left in it... and don't forget Linux has bugs leading to security vulnerabilities too!
A rough count of "named" CVE 10.0 score (or close to it) vulns in the last 5 years:
7 for Microsoft: ProxyLogon, ProxyShell, ProxyNotShell, LDAPNightmare, PrintNightmare, noPac, Follina
Windows has had a lot more named high-CVEs than that: MonikerLink, QueueJumper, Certifried, HiveNightmare...
As for "Linux", you'd need to specify the distro and environment, because Linux systems can be very different from one another. Your XZ example for instance didn't even affect most enterprise distros (like RHEL). regreSSHion didn't affect any musl libc distros like Alpine, but other systems would've also been unaffected had you set your LoginGraceTime to 0, which any sysadmin worth their salt would've done so. Leaky Vessels fails on SELinux enforcing distros (RHEL, Fedora etc) and sandboxed environments. I could go on, but you get the picture. Comparing the number of "Linux" vulnerabilities to Windows is completely pointless.
ClickFix which used Windows Update, and LNK that used Microsoft's signing keys, would disagree. There are still large and ongoing attacks that exploit Windows, and they are a serious problem - its just the attackers are less pointed at the everyday person, and more at corps and govs.
WannaCry was able to successfully run on ReactOS in 2025. Most other virsuses do tend to crash, because the memory layout is just a tiny bit different, but yeah, compatibility means compatibility. Lots of malware comes along for the ride.
However, there is a permissions layer that is more nix than Windows, which means the first foothold is still better than XP - you have to choose to execute the file. Self-running things don't tend to infect systems.
Its not a panacea, and there is a risk factor. And there aren't a lot of antivirus systems that can run correctly under ReactOS, because they freak out and think the OS is the malware, because they're scanning hashes for Windows, not another system.
But for a hobby OS, keeping hardware and software accessible after the rest of the world broke access, it still works.
Of course. Maybe not successfully but a "virus" is just software. If it runs software, it runs software, full stop. Maybe the same APIs are not available or behave differently, so it may be buggy or non-functional, but that's true of Half-Life here too.
Some, but not all, most don't. Ideally they would all work, ReactOS doesn't make a priority on being a "safer" option, just an open source option
Somewhere in the docs they state that they must also recreate whatever bugs the API has, otherwise applications written with those bugs as an (implicit) assumption could misbehave.
its worse than that, Windows activates/deactivates "bugs" based on the compatibility profile of the app.
so you can set an app to use a Windows XP compatibility profile, and this will simulate Windows bugs which were fixed in more recent versions of the OS
The payload yes, the exploit hopefully not.
Yes
You can run WannaCry under Wine, with a bit of effort.
Maybe worry about Linux malware which is a major problem right now everyone is in huge denial about, instead of throwing shade at a hobby OS emulating a 25 year old version of Windows.
ReactOS isn't the one that just had one of its package repos owned (again).
What's the major Linux malware problem that everyone is ignoring
AUR got hit recently [0], by what looks like more work of TeamPCP and friends.
EDIT: Worth noting, Arch ain't hosted on AUR. That's the community side only.
[0] https://archlinux.org/news/active-aur-malicious-packages-inc...
I would still note that this is not some kind of unique problem to Linux. There have been documented instances of malware making it to the Play Store, which is supposed to have a much more rigorous vetting process than AUR and costs actual money to publish on.
Just to expand... When the above user is comparing to Windows, who got most of the US government breached, I do think shade against AUR is uncalled for. Its just a community host for packages, comes with warnings, and isn't enabled by default, etc.
I can still happily upgrade via pacman without fear. Haven't been able to update on Windows without concern for over a decade - the malware comes builtin.
[0] https://www.cisa.gov/sites/default/files/2024-03/CSRB%20Revi...
Exactly.
I only have 4 packages installed with AUR and I think that’s the intention. You’re only going there when the other solutions aren’t available or don’t make sense.
Linux users used to say "Linux is secure and doesn't get viruses". Now the best thing we can say about it is "Linux gets viruses just like the Play Store". Sad if you ask me.
I think anyone who has made that claim was probably trying to be smug or didn’t actually understand security concepts, and was never correct to be making that claim.
Only Apple has made that claim in their marketing and that was 20 years ago when security by obscurity was shielding them, and when Windows XP was such a cesspool that anything with a normal amount of malware would look virus-free by comparison.
Isn't it funny how such incidents on Linux are rare enough that they make headlines, but on Windows that's been the baseline expected state of things for so long that nobody bats an eye anymore.
Btw if you're running an OS that's never had a malware incident, please, tell us!
Does Genode or Sculpt count? :)
https://genode.org
Conversely, this kind of attack: https://en.wikipedia.org/wiki/XZ_Utils_backdoor
...is essentially impossible to pull off against commercial operating systems, because their core components are all written in-house by staff with photo ID badges, details with HR, tax returns filed with the government, and a cubicle that makes sure that they're locals and not some faceless anonymous hacker identifiable by nothing other than a throwaway faked email address!
I get that there was a lot of "stigma" about open source, the world largely forgot about it, but... actually, in this sense of allowing anonymous contributions it remains a very real risk.
"Jia Tan" was almost certainly a paid professional hacker working for a nation-state actor. Their "helpful contributions" to XZ utils was nowhere near a full-time effort. They certainly had "other irons on the fire", most probably in the Linux kernel or immediately adjacent to it.
He's probably not the only one doing this kind of "work".
For all you know, Linux has more remote exploits purposefully baked into it than Windows has security bugs inadvertently left in it... and don't forget Linux has bugs leading to security vulnerabilities too!
A rough count of "named" CVE 10.0 score (or close to it) vulns in the last 5 years:
7 for Microsoft: ProxyLogon, ProxyShell, ProxyNotShell, LDAPNightmare, PrintNightmare, noPac, Follina
10 for Linux: XZ Utils, regreSSHion, Leaky Vessels, Copy Fail, PwnKit, Dirty Pipe, Looney Tunables, GameOver(lay), Baron Samedit, Sequoia
Windows has had a lot more named high-CVEs than that: MonikerLink, QueueJumper, Certifried, HiveNightmare...
As for "Linux", you'd need to specify the distro and environment, because Linux systems can be very different from one another. Your XZ example for instance didn't even affect most enterprise distros (like RHEL). regreSSHion didn't affect any musl libc distros like Alpine, but other systems would've also been unaffected had you set your LoginGraceTime to 0, which any sysadmin worth their salt would've done so. Leaky Vessels fails on SELinux enforcing distros (RHEL, Fedora etc) and sandboxed environments. I could go on, but you get the picture. Comparing the number of "Linux" vulnerabilities to Windows is completely pointless.
Windows stopped having serious malware problems at least 10 years ago
the ransomware campaigns would have happened on any OS enterprises use, because they were not security flaws in the OS
ClickFix which used Windows Update, and LNK that used Microsoft's signing keys, would disagree. There are still large and ongoing attacks that exploit Windows, and they are a serious problem - its just the attackers are less pointed at the everyday person, and more at corps and govs.