Does malware that comes through outdated apps go away if I uninstall the apps?

Question

I was reading this and this article.

The first article itself is about why software updates are extremely important for security, and the second one also mentions the following:

"Make sure your operating system, browsers, and plugins are always up to date, because keeping your software patched can keep online criminals at bay."

I have lots and lots of software that I never update like Adobe Acrobat PDF reader, Amazon kindle and whatnot. I never imagined that the consequences could be so threatening described in the first article I linked.

So a few days back I uninstalled all the old software that I didn't use/want.

1. Is it possible that malware can enter my PC through this outdated software? What happens when I uninstall the software? Does the malware go away with the uninstallation? We can take spyware as an example. If spyware came into my PC through such outdated software, will it have been removed if I uninstalled the software?

2. I ran my antivirus scan after I uninstalled the outdated software, and it showed my system is clean. I downloaded some other free anti-malware programs as well like Malwarebytes, HitmanPro, Avast... None of them detected any malware in my system except some PUPs. Is this reasonable to assume that my current antivirus is working perfectly as no malware was found that was able to dodge my current antivirus that couldn't dodge other anti-malware?

Answer 1

Is it possible that malware can enter my PC through this outdated software? What happens when I uninstall the software?

Yes. If the software have a handler that can be triggered by opening an attachment or a web page, malware can lead to the OS to open the vulnerable software and exploit it. If you uninstall the software, the port is closed, but malware that already exploited it will still remain on your computer.

If spyware came into my PC through such outdated software, will it have been removed if I uninstalled the software?

One of the phases of a malware infection is called persistence, and it does what it seems to: it will make sure it will run after the infection, even if you removed the outdated software. It can involve simple actions like putting a link on your Startup folder, creating registry keys, or be complex as replacing certain libraries with a tainted copy.

Is this reasonable to assume that my current antivirus is working perfectly as no malware was found that was able to dodge my current antivirus that couldn't dodge other anti-malware?

Absolutely not. Antivirus work by maintaining a database of known signatures and behavioral indicators for malware. What happened is that your system does not host any malware that your antivirus have a signature for.

A simple search for Fully Undetectable Malware will return lots and lots of hits, with hundreds of methods for calling sensible OS functions and still not trigger detection.

But unless your computer have special value to criminals, like being from a medium-large company or government, usually keeping the antivirus and antimalware updated are reasonable safe.

Answer 2

Can malware enter my PC through this outdated software?

If the software exposes network services, then most certainly. If not, then the attacker would have to find a way to trigger the outdated software. Like, emailing you an attachment that uses that software.

But entering your PC is just one factor to consider. Escalating access once on your PC is the other very real matter to consider. I can run a process that sends an exploit to this outdated software and gain persistent system access.

Malware doesn't "go away" just because you remove the vulnerable program that might have run it in the first place. Malware is, itself, a program. It would need to be removed.

Is it reasonable to assume that my current antivirus is working perfectly?

No.

Security has no silver bullet, or perfect solution, and no solution works perfectly 100% of the time. Security is about likelihoods and probabilities and confidence levels. You can be reasonably confident that no simple malware is on your system. A sufficiently complex bit of malware could still be there, but that's not nearly as likely.