Definition:
Malware is software or code created to perform harmful or unauthorized actions on a device, application, network, or data. It can steal information, monitor activity, alter files, encrypt content, disrupt services, or enable remote control of a system.
The term comes from the expression “malicious software” and covers threats with different behaviors and objectives. A virus is a type of malware, not a synonym for all malware. Not every error, pop-up advertisement, or loss of performance proves that an infection is present.
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How malware works
Malware can reach a system through attachments, links, manipulated programs, fake updates, removable devices, or unpatched vulnerabilities. Phishing is one method that can be used to induce someone to open a file or disclose credentials, but phishing and malware are not equivalent concepts.
Once executed, the code can perform one or more stages. Not every threat follows the same sequence, and some act immediately while others try to remain hidden for an extended period.
- Execution: The malicious code is activated through a user action, a vulnerability, or a compromised process.
- Persistence: It changes the system or uses legitimate mechanisms to run again after a restart.
- Privilege escalation and movement: It seeks higher permissions or tries to reach other computers and accounts on the network.
- Communication: It contacts command-and-control infrastructure to receive instructions or transfer information.
- Action on objectives: It steals, encrypts, modifies, or destroys data, displays advertising, consumes resources, or disrupts operations.
Some threats operate mainly in memory and use tools already present on the system. The absence of a recognizable file does not rule out malicious activity, just as the presence of an unknown file is not enough to classify it as malware.
Types of malware
Malware can be classified by its propagation method, technique, or intended effect. Categories can overlap, because a single campaign may combine several components or change behavior during an attack.
- Virus: Inserts itself into a host file or program and replicates when that element is executed or shared.
- Worm: Spreads between systems, usually through networks or vulnerabilities, without requiring a host file.
- Trojan: Presents itself as legitimate or useful software to encourage installation and then performs a hidden function.
- Ransomware: Locks systems or encrypts data and demands payment; some variants also steal information to increase pressure. Ransomware is therefore a specific category of malware.
- Spyware: Collects activity, credentials, or other data without valid authorization. Keystroke loggers can belong to this category.
- Malicious adware: Inserts advertising, changes the browser, or redirects traffic deceptively. Not all advertising-supported software is malware.
- Rootkit: Hides processes or components and helps maintain privileged access to a system.
- Bot: Turns the device into a remotely controlled node that can join a botnet to send spam, commit fraud, or participate in attacks.
These names describe functions rather than completely separate families. A Trojan can install spyware or ransomware, and a bot can incorporate rootkit techniques to make detection more difficult.
Effects on devices, data, and services
The effects depend on the permissions obtained, the systems affected, and how long the threat remains active. The impact can affect the confidentiality, integrity, and availability of information, as well as the operation of the device.
- Loss of confidentiality: Exposure of credentials, documents, communications, or personal data.
- Information alteration: Changes to files, settings, transactions, or records.
- Service disruption: Encryption, deletion, blocking, or resource consumption that prevents normal operation.
- Unauthorized use: Sending messages, committing fraud, mining cryptocurrency, or conducting attacks from the compromised device.
- Propagation: Access to other connected accounts, applications, or devices.
- Response costs: Investigation, recovery, notifications, business interruption, and control reviews.
Slow performance, crashes, and browser changes can be warning signs, but they can also have legitimate causes. Identification requires combining evidence, such as security alerts, unusual processes, unauthorized changes, abnormal connections, and file or log analysis.
Impact on websites and digital marketing
In a digital environment, malware can compromise a website, advertising accounts, measurement tools, or systems that store customer data. The problem is not limited to one person’s device, because a stolen credential can enable changes to shared services.
- Compromised websites: Injection of spam pages, payment-data skimming code, malicious downloads, or redirects to other domains.
- Advertising and analytics: Automated generation of false impressions, clicks, or conversions that distorts data and can create fraudulent spending.
- Email: Use of compromised accounts or domains to distribute malicious messages, with possible effects on sender reputation.
- Customer data: Access to, extraction of, or changes to personal and commercial information.
- Trust and visibility: Browsers, security providers, or search engines may display warnings or restrict access when they detect dangerous content.
Advertising fraud, spam, or a ranking decline can also have other causes. A marketing anomaly occurring at the same time does not by itself prove an infection, so security analysis should be separated from performance diagnosis.
Prevention, detection, and response
Protection against malware relies on several layers because no single tool detects every threat. Risk reduction combines technical controls, processes, and training, with measures adapted to the organization and the assets it needs to protect.
- Prevention: Security updates, restrictive configuration, least privilege, multifactor authentication, and control of applications and macros.
- Filtering and protection: Email and browsing security, endpoint protection, and a firewall configured for the network.
- Backups: Separate and tested versions that allow data to be recovered without relying on the affected system.
- Detection: Logs, alerts, behavioral analysis, and reviews of changes to files, accounts, and connections.
- Response: Isolation of affected systems, preservation of evidence, scope analysis, removal or rebuilding, and validated recovery.
Response does not end when a detected file is deleted. It is necessary to determine how the threat entered, which credentials and data it could reach, and whether other access mechanisms remain. Depending on the incident, notifications, credential changes from clean systems, and subsequent monitoring for recurrence may also be required.