Beware the signs of a potentially malware-infested PC: slower-than-usual performance, the recent occurrence of lots of pop-ups, and other weird issues. It’s possible your system has been infected by a virus, spyware, or other nefarious entity—even if you have an antivirus program installed. Yes, out-of-the-ordinary behavior is sometimes the result of hardware issues, but it’s best to first rule out malware if your PC is acting up. Here’s a step-by-step guide for taking action.

Step 1: Enter Safe Mode

Before you do anything, you need to disconnect your PC from the internet, and don’t use it until you’re ready to clean your PC. This can help prevent the malware from spreading and/or leaking your private data.

If you think your PC may have a malware infection, boot your PC into Microsoft’s Safe Mode. In this mode, only the minimum required programs and services are loaded. If any malware is set to load automatically when Windows starts, entering in this mode may prevent it from doing so. This is important because it can make removing the nefarious files easier since they’re not actually running or active.

You may find that your PC runs noticeably faster in Safe Mode. This could be a sign that your system has a malware infection, or it could mean that you have a lot of legitimate programs that normally start up alongside Windows. If your PC is outfitted with a solid-state drive it’s probably fast either way.

Step 2: Delete temporary files

Now that you’re in Safe Mode, you’ll want to run a virus scan. But before you do that, delete your temporary files. Doing this may speed up the virus scanning, free up disk space, and even get rid of some malware. To use the Disk Cleanup utility included with Windows 10 just type Disk Cleanup in the search bar or after pressing the Start button and select the tool that appears named Disk Cleanup.

Step 3: Download malware scanners

Now you’re ready to have a malware scanner do its work—and fortunately, running a scanner is enough to remove most standard infections. If you already had an antivirus program active on your computer, you should use a different scanner for this malware check, since your current antivirus software may not have detected the malware. Remember, no antivirus program can detect 100 percent of the millions of malware types and variants.

There are two types of antivirus programs. You’re probably more familiar with real-time antivirus programs, which run in the background and constantly watch for malware. (Another option is an on-demand scanner, which searches for malware infections when you open the program manually and run a scan. You should have only one real-time antivirus program installed at a time, but you can have many on-demand scanners installed to run scans with multiple programs, thereby ensuring that if one program misses something a different one might find it.

Step 4: Fix your web browser

Malware infections can damage Windows system files and other settings. One common malware trait is to modify your web browser’s homepage to reinfect the PC, display advertisements, prevent browsing, and generally annoy you.

Before launching your web browser, check your homepage and connection settings. For Internet Explorer right-click the Windows 10 Start button and select Control Panel, then Internet Options. Find the Home Page settings in the General tab, and verify that it’s not some site you know nothing about. For Chrome, Firefox, or Edge, simply go to the setttings window of your browser to check your homepage setting.

If you’ve noticed any unexpected reboots or PC instability as a result of the recent Spectre patches, there’s a solution: Microsoft has issued an emergency Windows patch that rolls back the recent Spectre mitigations.

Confused? It’s a bit complicated. After the intial Spectre and Meltdown vulnerabilites were disclosed, both Intel and Microsoft hustled out patches to mitigate the problem. Unfortunately, Intel’s latest microcode updates—and the BIOS updates from PC makers based upon them—were themselves buggy, causing instability, reboots, and data loss in some PCs.

Microsoft’s latest patch (KB4078130) allows people with affected systems to download the patch via the Microsoft Update Catalog, which disables the mitigations for the “Spectre variant 2.”

Note that the patch notes specifically state that you should run this patch “if you are running an impacted device” (emphasis ours). In other words, if your system is working normally, don’t bother downloading this patch. This is what Microsoft calls an “out of band” patch, and it doesn’t appear that it will be made available via Windows Update, either.

Why should you consider it? Intel has warned previously that the faulty patch can sometimes cause data loss and corruption, and Microsoft is saying the same: “Our own experience is that system instability can in some circumstances cause data loss or corruption,” the patch notes state.

There’s another wrinkle, though. As part of the patch, Microsoft is allowing users to edit the Windows registry to toggle the mitigations on or off. (Instructions are here.) It’s possible to toggle Microsoft’s patch off, and then, when Intel solves its own patching problem, re-enable it. That scenario is actually what Microsoft recommends—again, only if you’ve noticed system instability and want to take action against it.

Toggling the mitigations on and off is also a feature of the latest InSpectre utility.

What should you do? There’s no one-size-fits-all answer to this question. But we can tell you what we’re doing: if a PC is working as expected, we’re leaving it patched and in place. If you’re backing up your data (to the cloud or an external drive) chances are your most crucial data will be saved in case your system goes down unexpectedly. Obviously, install Microsoft’s emergency Windows patch if you’re running into system issues. There’s no perfect solution—if you’re more paranoid than we are, feel free to deploy the patch even if your PC hasn’t hiccuped.

Good luck, and be sure to check out PCWorld’s guide on how to protect your PC against Meltdown and Spectre. Operating system updates are just one part of it.

As Bleeping Computer noted, system makers such as Dell and HP also advise rolling back their own BIOS patches to an earlier version, which they’re redeployed. It’s all horrendously confusing for consumers and IT organizations alike. Fortunately, at least, there haven’t been any public cases of these vulnerabilities being exploited, Microsoft says.