I'm a Linux user and I installed Windows recently, I need it for some software. I don't want to use any anti-malware programs, I don't plan on giving administrative rights to applications I don't trust - just like in Linux. So, in theory, getting a malware shouldn't be possible, right?
So, my question is, can I get infected if I don't give admin privileges to untrusted programs? If so, how?
Yes. It can infect you nonetheless.
Using a non-administrative account only keeps malware from spreading to other users in the system, and it's a good practice regardless of everything else.
But aside from that, The malware can do everything your user is allowed to do, because it is a program like every other: it could create and modify files, open sockets, log your Keys, post malicious content on your social network profile, spam your contact list..
Then, there is privilege escalation: a bug in a piece of software, a misconfigured service, or any known or yet-to-be-known vulnerability in windows could elevate the malware privileges to administrative, just like it happens on unix systems.
Sorry, there is a bit of misinformation here.
Most current malware does not need admin privs (or „high integrity“). Without admin privs it can copy itselt to your „home directory“, make itself persistent, get read access to all your data, write access to most of your data, internet access, etc. There are even legitimate programs that happily install without admin rights or Elevation prompts.
UAC (this sudo-like concept we have since windows Vista) can be bypassed in most cases when you account has admin rights. Most bypasses abuse how microsoft gives special trust to some of it’s own programs. But most malware either doesn‘t bother or the author doesn‘t know how. Anyway, malware does not need admin rights to e.g. encrypt all your photos for ransom.
still, UAC does not hurt.
the antivirus built into windows has become quite capable. If you don‘t click on suspicious emails or download and run suspicious stuff, going without antivirus is a viable option. If you want more protection and don‘t want to spend money, i recommend the free version of avira.
if you want to run software you don’t completely trust, VMs (or at least sandboxie within windows) are the way to go. The probability of your windows malware escaping VirtualBox into your linux system is pretty much zero, especially if you reset your VM to a known safe state after you are done.
As CodesInChaos and Rory Alsop have mentioned, it's more about the programs on your computer than the malware itself. What you plan on doing ("I don't plan on giving administrative rights to applications I don't trust") would get in the way of generic Trojans, but that is only one kind of malware. Here is an example that could get around that strategy: you give a program that is legitimate admin rights, and then an attacker buffer overflows it and overwrites the EIP to point to whatever malware he has on your machine. And that's it, admin access for the hacker. The bottom line: Any program that runs as admin has the potential to give an attacker admin access, assuming they already have some level of access to your computer.
For practical purposes, the vast majority of malware that is out there will simply fail to install or work at all if it doesn't have administrator access.
Now there are some pieces of malware out there that will take advantage of the restricted environment and do what it can. In fact, the restricted environment allows a lot to be done. It can install a keylogger to monitor all key presses, including programs that are running as a different user that you started by right clicking Run-As. Depending on the situation and possibly Windows version, it can also record the password that you enter when you use Run-As. Most likely any passwords that you entered in to your browser and other applications can be intercepted.
One advantage of using a limited user account is that it increases the effectiveness of anti-virus software. It often takes many days or a few weeks for virus definitions to recognize new malware. If that new malware is contained in a limited account then your AV software can find it later. If it's allowed to get in to your Administrator account and cloak itself then it's too late.
