How to Detect and Remove Malware from Your Network

Malware does not announce itself. It hides in legitimate-looking processes, moves laterally between machines, and often operates for weeks or months before anyone notices. According to IBM’s Cost of a Data Breach Report, the average time to identify a breach is 194 days. For a Los Angeles business handling client data, financial records, or intellectual property, that is an unacceptable window of exposure.

Detecting and removing malware requires a systematic approach. Here is how to recognize the warning signs, contain an active infection, and clean your network without making the problem worse.

Common Signs Your Network Is Infected

Malware rarely produces a single obvious symptom. Instead, it creates patterns of unusual behavior that are easy to dismiss individually but alarming in combination. Watch for machines that suddenly run slower than usual or consume excessive CPU and memory, unexpected spikes in outbound network traffic especially during off-hours, employees being locked out of accounts or seeing unfamiliar login attempts, antivirus software that disables itself or cannot update, and files that appear encrypted, renamed, or missing without explanation.

The Cybersecurity and Infrastructure Security Agency maintains an updated list of common malware indicators that every IT team should reference. A single symptom might mean nothing. Three or four together warrant immediate investigation.

How Malware Gets Into Business Networks

Understanding entry points helps you investigate and prevent future infections. The most common vectors for business networks include phishing emails with malicious attachments or links, compromised websites that exploit browser vulnerabilities, infected USB drives or external devices, unpatched software with known vulnerabilities, and stolen or weak credentials used to access remote services.

The NIST Cybersecurity Framework emphasizes that identifying and protecting against these entry points is the foundation of any security program. Most malware infections trace back to one of these five vectors, so your investigation should start there.

Step 1: Isolate the Affected Systems

The moment you suspect a malware infection, your first priority is containment. Disconnect the affected machine from the network immediately, either by pulling the Ethernet cable or disabling the wireless adapter. Do not power the machine off, as some malware resides only in memory and shutting down destroys forensic evidence you may need later.

If multiple machines show symptoms, isolate the entire network segment. Disable the switch port or VLAN rather than trying to identify every compromised device individually. Speed matters here because many malware variants spread laterally within minutes of initial execution.

Step 2: Identify the Type of Malware

Different malware types require different response strategies. Ransomware encrypts files and demands payment, which means you need to identify the specific variant before deciding whether recovery from backups is your only option. Trojans and remote access tools give attackers persistent access to your systems, meaning containment must include credential resets across the environment. Worms replicate automatically across the network, so isolation of every potentially affected segment is critical before cleanup begins.

Use your endpoint detection and response tools to analyze the malware’s behavior, file hashes, and network connections. Cross-reference findings with threat intelligence databases like MITRE ATT&CK to understand what the malware is designed to do and what else it may have already accomplished.

Step 3: Assess the Scope of the Infection

Before you start removing malware from one machine, determine how far it has spread. Scan every device on the network using updated antivirus signatures and endpoint detection tools. Review firewall and DNS logs for connections to known malicious IP addresses or domains. Check Active Directory logs for unusual account activity, privilege escalation, or new accounts created without authorization.

This assessment phase is where most businesses make a critical mistake: they clean the one machine they found and assume the problem is solved. Malware authors design their tools to persist across multiple systems. If you miss even one compromised device, the infection will return.

Step 4: Remove the Malware

Once you have identified every affected system and understand the malware type, begin the removal process. For machines with endpoint detection and response tools, use the quarantine and remediation features built into the platform. For heavily compromised systems, a complete reimage from a known-clean backup is safer and faster than trying to surgically remove every malicious file.

Reset all passwords for accounts that were active on compromised machines, starting with administrator and service accounts that have elevated privileges. Revoke and reissue any authentication tokens or certificates that may have been exposed. The United States Computer Emergency Readiness Team publishes specific remediation guidance for widely distributed malware variants.

Step 5: Verify the Network Is Clean

After removal, monitor the network intensively for at least two weeks. Reinfection often occurs within the first 48 to 72 hours if any compromised system was missed during the cleanup phase. Run full scans on every endpoint daily during this period. Monitor DNS queries and outbound connections for any communication with command-and-control infrastructure.

Deploy network-level detection tools that watch for lateral movement patterns, unusual authentication behavior, and data exfiltration attempts. If you do not have these capabilities in-house, this is the time to engage a managed detection and response provider who can monitor your environment around the clock.

Preventing the Next Infection

Removing malware is a reactive exercise. The real value comes from closing the gaps that allowed the infection in the first place. Implement or strengthen endpoint detection and response across every device, enforce multi-factor authentication on all remote access and privileged accounts, establish a patch management program that addresses critical vulnerabilities within 48 hours, deploy DNS filtering to block connections to known malicious domains, and conduct regular security awareness training so employees can recognize phishing attempts before they click.

The FBI Internet Crime Complaint Center reports that business losses from malware and related cyberattacks exceeded $12.5 billion in 2023 alone. Most of those losses were preventable with the controls listed above.

When to Call in Professional Help

If the malware has encrypted critical data, if you cannot determine how far the infection has spread, or if the attack involves regulatory notification requirements, bring in professional incident response support immediately. Attempting to handle a complex malware incident without the right expertise often extends the recovery timeline and increases the total cost.

For businesses that lack dedicated security staff, a managed IT provider with incident response capabilities can serve as your first line of defense and your recovery team when something gets through.

We Solve Problems helps Los Angeles businesses detect, remove, and prevent malware infections with 24/7 monitoring, endpoint protection, and incident response support. Get a free security assessment to find out where your network is vulnerable.