How to Tell if Your Employees’ Devices Are Infected with Malware

I just returned from DefCon, and I’m still buzzing about the hardware hacking village—some of the attacks I saw there were downright creepy. And here’s the issue: most businesses don’t know what lies waiting on their employees’ devices.

Malware is evolving. It’s sneakier, more gnarly, and often entirely invisible to the average user. You may believe that your security stack is solid, but I’ve seen malware get past even so-called “AI-powered” solutions. So how can you tell if the devices used by employees—laptops, desktops, mobiles—have been compromised? Buckle in. I’ve been at this since 1993, when we were still dialing in on PSTN lines and routing voice and data through muxes. I’ve witnessed everything from the Slammer worm causing chaos to the intro of modern-day zero-trust architectures in large banks. I know what a proper infection looks like, and I know how to look for it.

Quick Take

Short on time? Here’s a rapid-fire rundown of how to ensure employee devices are free of malware:

• Weird system slowdowns? Or malware spamming your CPU or RAM.
• Random pop-ups? If ads appear on a work laptop — something’s broken.
• Weird domains being talked to by devices? Time to check DNS logs.
• AV alerts getting disabled? That’s textbook malware behavior.
• Random executables showing up? Red flag. System-critical folders especially.
• Unusual outbound traffic? Malware thrives on quietly exfiltrating data.

Now, let’s get down to the details.

Signs of Malware on Devices

The challenge of contemporary threats? Malware does not always reveal itself. Is kinda not like before, when you got 50 popups saying your windows XP had 9999 viruses. Today’s malware is hidden, persistent, and often only becomes evident when it’s too late.

Watch out for:

• Programs Slowing Down or System Lagging: If a generally sprinting device suddenly lags, malware could be hogging resources.
• Amount of Network Traffic: An unusual increase in the size of outbound traffic—particularly to unknown endpoints—could indicate the malware is removing data.
• Security Features Disabled: Is Windows Defender, antivirus and EDR tools suddenly disabled—if so that’s a big red flag.
• Phantom processes in task manager: Check for strange processes running under “SYSTEM” or “svchost. exe” with no good reason.
• Unexpected Files & Registry Changes: Malware can change your startup files, or can reside in obscure registry keys.

And mobile devices are not immune either — if an employee’s phone battery seems to discharge faster than normal, gets too hot or keeps crashing, they may have malware running in the background harvesting data.

Running Security Scans

Listen, putting “antivirus” on your computer is not sufficient. You need layered detection. We at PJ Networks deploy behavior based detection in addition to signature based AV. But if you are stuck with old-school ways, here’s what you can do:

1. Full-System AV Scan – Perform a full, deep scan (not a quick scan). But be warned, modern malware can evade traditional AV.
2. EDR/XDR Analysis – If you have EDR (like XDR as well), they can be used to check on processes activity, commands execution or any unusual access to files.
3. Network Traffic Monitoring – Review firewall logs and SIEM alerts for connections to suspicious IPs.
4. Memory & Process Analysis — Explore alive processes directly using tools such as Process Hacker or Sysinternals Suite.
5. Sandbox Testing – If you believe a file to be malicious, DO NOT open it on the machine of an employee. Instead, consider using an isolated sandbox.

Must Read: If you have trouble downloading or running scans, boot into Safe Mode—it’s common for malware to disable your security goodies upon normal boot.

Enterprise Level Endpoint Security Strategy

If your company keeps only antivirus in arsenal, we have to talk. These days, endpoint protection goes beyond just running scans for malware.

Here is what every organization must do:

1. Implement Zero-Trust Security: I helped three banks recently implement their zero-trust architecture, and the difference was like night and day. Zero-trust means that no device, no user, no process is trusted by default—everything gets authenticated, verified, and monitored.
2. Endpoints Detection & Response (EDR/XDR): Traditional AV simply compares malware with a database. EDR does much more—it monitors attack behaviours and detects anomalies, providing visibility of everything that happens on a device. You are already behind if your IT team isn’t analyzing endpoint telemetry already.
3. Separation of critical IT resources: It is important to keep critical IT resources separated, limiting the potential of threat propagation. Malware requires communications paths to function (command-and-control servers, data exfiltration endpoints). Knock it out at the DNS level, and you stop entire families of malware from even damaging you.
4. Routine Security Health Checks: The vast majority of businesses have no visibility into their attack surface. Perform regular vulnerability scans, endpoint assessments, and red team penetration tests (yes, even on employee workstations).
5. Device Hardening & Least Privilege Access: Disable USB autorun (malware loves USB drives). Disable unwanted system services. Use least-privilege user accounts—absolutely no one should have admin rights unless they need them.

Malware Detection Solutions By PJ Networks

Employee devices security at PJ Networks is a high priority. We deploy enterprise-wide endpoint security solutions that are designed to detect, isolate, and eradicate the malware before it does any damage.

What we offer:

• EDR & MDR Security Solutions — Advanced endpoint telemetry to investigate and eliminate suspicious activity.
• SIEM Monitoring & Threat Hunting – We proactively search for threats within company networks
• Network Segmentation & Firewall Security – Preventing the lateral spread of infections.
• Incident Response & Forensics – If you are infected, we reverse engineer it, quarantine it and ensure you are not reinfected.

We don’t trust “AI-powered” buzzword solutions. We rely on real-world threat intelligence and tried and true detection methodologies — because when it comes to keeping a business secure, there is no magic button. Just smart, layered defenses.

Conclusion

Malware isn’t going away. It’s only getting sneakier. And employee devices? They’re a top entry point that attackers exploit to get into networks. If you’re not constantly monitoring every single device within your environment — and that includes mobile phones — you’re leaving your company very exposed to threats.

So, what’s next? Run security scans, begin with zero-trust vis-a-vis your vendors, and take endpoint security seriously. Or the companies that try to wait until after they have an infection? They usually regret it. Would you like to learn more about how PJ Networks can secure your environment? Let’s talk.