How to tell if you’ve been infected with malware

Malware can manifest in a variety of ways, impacting system performance, security, and user experience. Here are the most common indicators from a user’s perspective.

System Performance Issues

• Sudden slowdowns in your device’s performance, such as programs taking longer to load or respond, are a classic sign of malware consuming system resources in the background.
• Frequent system crashes, freezing, or the appearance of the “blue screen of death” (BSOD) often signal that malicious processes are overwhelming your operating system.

Unusual Pop-Ups and Ads

• Unexpected pop-up ads, especially when you’re not actively browsing, are often linked to adware or potentially unwanted programs (PUPs).
• Fake antivirus warnings or system alerts appearing without cause are also red flags.

Browser and Application Changes

• Your browser’s homepage or search engine changes without your consent, or you notice new toolbars, extensions, or apps you didn’t install.
• Frequent redirection to unfamiliar or spoofed websites, often designed to steal your credentials or personal information.

Unexplained Network and Internet Activity

• A sudden spike in internet usage or network activity, particularly during idle times, can indicate malware is transmitting data or communicating with external servers.
• High CPU or disk usage by unknown processes, observable in Task Manager or similar system monitors.

Missing or Altered Files

• Files randomly disappearing, being renamed, encrypted, or modified without your action can be a sign of ransomware or other destructive malware.
• Loss of disk space due to hidden or bloated malicious files.

Disabled Security Measures

• Security software, such as antivirus or firewall, is disabled or cannot be turned back on, often as a result of malware trying to avoid detection.
• System tools like Task Manager or Registry Editor are inaccessible.

Unauthorized Activity and Access

• New, suspicious applications or browser extensions appear without your knowledge.
• Alerts about unauthorized login attempts, unknown devices accessing your accounts, or outbound communications to unfamiliar IP addresses.

Device-Specific Symptoms

• On mobile devices: rapid battery drain, overheating, apps opening or crashing without input, spikes in data usage, or contacts receiving strange messages from your device.
• Camera or microphone indicator lights remain on when not in use, suggesting remote access by malware.

Financial or Account Compromise

• Unauthorized financial transactions, increased spam emails sent from your account, or ransom notes demanding payment for file decryption.

Technical indicators of malware infection (Indicators of Compromise or IOCs)

Technical indicators—often called Indicators of Compromise (IOCs)—are specific, observable artifacts or patterns that signal the presence of malware on a system or network. These indicators are used by security professionals and tools to detect, analyze, and respond to threats.

File-Based Indicators

• Unusual or suspicious file names, new files in unexpected locations, or files with non-standard extensions (e.g., encrypted files with strange extensions from ransomware).
• File hashes (MD5, SHA-1, SHA-256) that match known malware signatures.
• Unexpected modifications to system files, registry entries, or configuration files.

Process and System Behavior

• Unknown or suspicious processes running in memory, especially those consuming high CPU or memory resources.
• Processes or services with names similar to legitimate ones but with subtle differences (typosquatting).
• Persistence mechanisms, such as new entries in autostart locations or scheduled tasks that re-launch malware after reboot.

Network-Based Indicators

• Communication with known malicious IP addresses or domains, often detected via firewall or IDS/IPS logs.
• Unusual outbound traffic, including data exfiltration or command-and-control (C2) communications.
• Unauthorized network scans or spikes in web traffic to/from specific addresses.
• Unexpected DNS requests or connections to suspicious domains.

System and Security Changes

• Disabling or tampering with security tools (antivirus, firewall, EDR).
• Inaccessible or altered system tools (Task Manager, Registry Editor).
• New or unauthorized user accounts created on the system.

Mass File Operations

• Bulk file renames, deletions, or encryptions—especially indicative of ransomware.
• Sudden changes to large numbers of files within a short period.

Sandbox and Behavioral Analysis

• Malicious files exhibiting harmful behavior when executed in a sandbox environment, such as attempting to modify system files, escalate privileges, or connect to external servers.

Resource Consumption

• Unusual spikes in CPU, memory, or network usage, often due to malware activities like cryptomining, data exfiltration, or DDoS participation.