Common cybersecurity threats include phishing, malware, ransomware, password attacks, denial-of-service attacks, man-in-the-middle attacks, insider threats, and software vulnerabilities or unauthorized access. These categories overlap rather than form a definitive ranking: a phishing message, for example, can steal a password or deliver malware. The practical response is to use strong account protections, keep software updated, handle unexpected requests cautiously, and maintain backups you can restore.
What makes a cybersecurity threat risky?
A threat is not dangerous simply because it has a technical name. Risk depends on whether an attacker can exploit a weakness, what systems or information are exposed, and what harm follows. CISA’s NG9-1-1 Cybersecurity Primer provides examples of threats in a critical-infrastructure setting; it is a taxonomy, not a measure of how often consumers encounter each one. The eight categories below are an illustrative selection, not a universal “top eight.”
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Some are methods of gaining access, some describe malicious software, and others describe the effect on a service. They can occur together: ransomware is malware, and phishing can be a way to deliver it or obtain credentials.
1. Phishing and social engineering
Phishing uses deceptive messages, links, emails, or attachments to persuade someone to reveal information, open harmful content, or install malware. Social engineering is the broader manipulation of people into taking an action that benefits an attacker. CISA summarizes phishing this way: “Phishing happens when attackers trick people into clicking harmful links, opening fake emails or downloading malicious attachments.” The sentence appears in CISA’s Four Cybersecurity Essentials for SLTTs, published August 29, 2025.
Not every attempt is obvious. A message may imitate a familiar organization or arrive in the middle of a real conversation. Pause when a request is unexpected, especially if it asks for credentials, payment, sensitive information, or an urgent change. Verify through a separate, trusted channel rather than relying on the message’s link or contact details. Report suspicious messages using the email service’s reporting feature or your workplace’s process.
2. Malware
Malware is a broad term for malicious software. It can access, read, change, or steal stored data, compromise a device, or disrupt its normal use. A virus is one kind of malware, not a synonym for all malicious software. Malware may arrive through a deceptive attachment or download, among other routes; avoiding suspicious links helps, but no single habit eliminates the risk.
CISA’s device-data guidance discusses malware and protecting data stored on devices. Keep your operating system and applications updated, and use the security protections recommended for your device. If you suspect a device is compromised, avoid entering more passwords or sensitive information on it and follow the device maker’s or your organization’s incident guidance.
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3. Ransomware
Ransomware is malware that can deny access to a device or data, often by encrypting files. Some attackers also steal data and threaten to publish it, a tactic sometimes called double extortion. That means an incident can involve both loss of access and exposure of information.
Paying a ransom does not guarantee that files will be restored or that stolen data will be deleted. Preparation and recovery matter: maintain backups, know how to restore them, and keep them protected from the devices they back up. CISA’s StopRansomware Guide, prepared with the FBI, NSA, and MS-ISAC, sets out prevention and response recommendations, including phishing-resistant MFA for important services such as email and VPNs.
4. Credential and password attacks
Attackers may use weak or guessable passwords, reuse credentials exposed elsewhere, or obtain login details through phishing. A stolen password can be especially damaging when it also works on other accounts. Strong, unique passwords reduce the value of guessing or credential reuse, but they do not make an account invulnerable.
- Use a different, long password for each important account. A password manager can help create and store unique passwords.
- Turn on multifactor authentication (MFA), especially for email, financial, and work accounts. MFA adds a verification step beyond the password.
- Choose phishing-resistant MFA when a service supports it, particularly for accounts with access to critical systems. Check the service’s current options and device compatibility.
- Do not approve an unexpected sign-in prompt or share a one-time code in response to an unsolicited request.
CISA’s Secure Our World guidance recommends strong passwords or a password manager, MFA, and recognizing and reporting phishing. Its audience and recommendations are broader than any single consumer product or service.
5. Denial-of-service and distributed denial-of-service
A denial-of-service (DoS) attack overwhelms a network or service’s resources so that normal users have difficulty accessing it. A distributed denial-of-service (DDoS) attack sends traffic from many systems rather than a single source. The primary effect is reduced availability or an outage; DoS is not, by definition, a method of stealing stored data. A CISA primer gives network overload as an example, while its older, sector-specific healthcare assessment lists DDoS among threat examples.
For an individual user, the immediate sign may simply be that a website or service is unavailable. If you operate an online service, mitigation generally requires provider or organizational measures; repeated refreshing is not a remedy for an attack.
6. Man-in-the-middle attacks
In a man-in-the-middle attack, an attacker secretly relays—and may alter—communications between two parties who believe they are communicating directly. Intercepted information could be exposed, or messages could be changed. The NICCS glossary defines the term, and CISA’s NG9-1-1 primer describes interception and monitoring as an example.
Use secure, trusted connections for sensitive activity and pay attention to browser or app security warnings rather than bypassing them. The exact protections depend on the service and network; the attack is about interference with communications, not simply being connected to public Wi-Fi.
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An insider threat involves risk from someone with authorized access, such as an employee or contractor, who may steal, corrupt, or destroy data. Not every incident is malicious: mistakes or mishandled access can also create exposure. CISA includes insider threats in its infrastructure primer and threat scenarios, but those examples do not establish a current frequency estimate for organizations or consumers.
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Organizations can reduce potential harm by granting only the access each person needs, reviewing permissions, and removing access when it is no longer required. For individuals, follow workplace data-handling rules and report unexpected access or disclosure through the appropriate channel.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.8. Software vulnerabilities, spoofing, and unauthorized access
A software vulnerability is a weakness that could be exploited to compromise a system. CISA’s healthcare-sector assessment lists software vulnerabilities and SQL injection as examples; SQL injection is an attack that exploits weaknesses in how an application handles database input. The assessment is from 2010 and is sector-specific, so it should not be read as a current measure of risk.
Spoofing and unauthorized access are related access concerns, but they are not identical to software vulnerabilities. CISA’s NG9-1-1 primer describes spoofing as an unauthorized device masquerading as an authorized one and also lists unauthorized network access. A vulnerability can enable access, while spoofing misrepresents identity or authorization. Keeping software updated helps address known weaknesses; organizations also need appropriate access controls and monitoring.
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How to protect data stored on your devices
Use several complementary safeguards rather than relying on one defense. CISA guidance for state, local, tribal, and territorial governments identifies phishing training, strong passwords, MFA, and software updates as foundational practices; these are broadly useful habits even though that fact sheet is aimed at government organizations.
- Update your operating system, browser, and apps when updates are available.
- Use unique passwords, a password manager, and MFA for important accounts.
- Check unexpected requests through a separate trusted channel; report suspicious messages.
- Back up important files and confirm that you can restore them.
- For work devices or accounts, follow your organization’s security and incident-reporting process.
Choose a backup destination you can recover from
CISA names a secure external hard drive and a properly vetted cloud service as backup options. Neither is universally better; consider whether the backup is separated from the device, protected from unauthorized access, and practical to restore when needed.
| Option | What to consider |
|---|---|
| Secure external drive | Keep it protected and separate from the device when it is not being used for backup, so a problem affecting the device is less likely to affect the backup too. |
| Properly vetted cloud service | Review the service’s security and account protections, and make sure you know how to retrieve your files if you need them. |
A backup is useful only if it is available and usable during recovery. Follow the service or device instructions to test restoration. CISA’s data protection guidance covers these backup approaches; a backup destination by itself does not prevent ransomware or other compromise.
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