12 Common Network Security Threats and How to Fix Them

Last updated: October 2026. Written by Josh Hutcheson, OnlineCourseing editor. Every statistic below was re-read at its source (IBM, Verizon, CISA, the U.S. Bureau of Labor Statistics) on 24 October 2026. See our review methodology.

QUICK VERDICT

What are network security threats?

A network security threat is anything that could let someone read, change, steal or block data and systems on a network without permission. Some threats are software (malware such as viruses, worms, trojans and ransomware); some are techniques aimed at people (phishing and other social engineering); some exploit weaknesses in software or configuration (unpatched systems, exposed services, weak passwords); and some come from inside the organization. A threat is the potential danger, a vulnerability is the weakness it uses, and the risk is how likely and how damaging the combination is.

Why this matters: IBM’s Cost of a Data Breach Report 2026 puts the global average cost of a breach at $4.99 million, a 12% increase on the previous year and a record high, and reports a 56% increase in AI-driven attacks, led by deepfake impersonation and AI-enabled malware. The list below covers the twelve threats that cause most of that damage, how each one works at a high level, and what to do about it.

The 12 most common network security threats at a glance

1. Exploited software vulnerabilities

The biggest change in recent years: software vulnerabilities have overtaken stolen passwords as the top way attackers get in. Verizon’s 2026 DBIR found that 31% of breaches start with exploiting a software flaw, as attackers shift from tricking people to exploiting systems. Edge devices such as VPN appliances, firewalls and file-transfer servers are frequent targets because they face the internet and are often patched late.

How to fix it: keep an inventory of everything internet-facing, patch on a schedule measured in days for critical flaws, and prioritize using CISA’s Known Exploited Vulnerabilities (KEV) catalog, which lists flaws attackers are actually using. Turn off services you do not need and put admin interfaces behind a VPN.

2. Phishing

Phishing is a message that impersonates someone trusted, such as a bank, a supplier, a colleague or IT support, to get the recipient to click a link, open an attachment, enter a password or approve a payment. It now arrives by text message (smishing), voice call (vishing), QR code and collaboration apps as well as email. Verizon reports that mobile phishing gets about 40% higher click rates than email, which is why attackers are moving to phones.

How to fix it: email filtering with sender authentication (SPF, DKIM and DMARC), regular short training with realistic examples, an easy “report phishing” button, and multi-factor authentication so a stolen password alone is not enough. For the accounts that matter most, use phishing-resistant MFA such as security keys or passkeys.

3. Ransomware

Ransomware encrypts an organization’s files and systems and demands payment for the key, and most groups now also steal data first and threaten to leak it. Verizon’s 2026 report found ransomware in 48% of breaches, but ransom payouts are shrinking and more victims are refusing to pay. It usually arrives through one of the other threats on this list: an exploited vulnerability, a phishing email or stolen remote-access credentials.

How to fix it: keep backups that are offline or immutable and test that you can restore them; segment the network so one infected machine cannot reach everything; use endpoint detection and response (EDR); and remove or lock down remote desktop exposure. Have an incident response plan written before you need it.

4. Stolen and weak credentials

Many breaches need no malware at all: the attacker simply logs in. Passwords are stolen by phishing and malware, reused from other breached sites (credential stuffing), or guessed because they are weak. Once inside with a valid account, an attacker looks like a normal user, which makes detection slow.

How to fix it: require MFA everywhere, starting with email, VPN, cloud admin and finance systems; give staff a password manager; block known-breached passwords; and follow least privilege so most accounts cannot reach sensitive systems even if compromised.

5. Viruses and worms

A virus attaches itself to a legitimate file or program and spreads when that file is shared or run. A worm spreads by itself across a network by exploiting a vulnerability, with no user action, which is why worms can move very fast. Both can corrupt data, steal information or carry other malware such as ransomware. Modern variants change their code to evade simple signature-based antivirus.

How to fix it: modern endpoint protection on every device, prompt patching (worms depend on unpatched flaws), and network segmentation to limit how far an outbreak can spread.

6. Trojans

A trojan is malicious software disguised as something legitimate: a fake software update, a cracked app, a browser extension, an invoice or a game mod. Once installed it can steal data, log keystrokes, open a back door for remote access or download further malware. Fake ads and search results that point to look-alike download sites are a common route.

How to fix it: limit who can install software, use application allow-listing on business machines, download only from official sources, and keep endpoint protection running.

7. Spyware and keyloggers

Spyware quietly collects information about a person or organization and sends it to a third party. Keyloggers, a common type, record keystrokes to capture passwords, card numbers and messages. Infostealer malware, which harvests saved browser passwords and session cookies, is now one of the main sources of the stolen credentials that fuel threat #4.

How to fix it: endpoint protection, not saving business passwords in personal browsers, MFA so captured passwords are not enough, and short session lifetimes for sensitive apps.

8. Rootkits

A rootkit is malware designed to hide itself and other malicious programs from the operating system and security tools, giving an attacker long-term, privileged control of a machine. Because it runs at a low level, sometimes below the operating system, it is very hard to detect and remove once installed.

How to fix it: enable secure boot and firmware protections, keep operating systems patched, use EDR that looks for suspicious behavior rather than only known files, and when a rootkit is suspected, rebuild the machine from a clean image rather than trying to clean it.

9. Social engineering beyond email

Social engineering is any trick that manipulates a person into breaking security: a caller pretending to be IT who asks for a password “to run some updates,” a fake supplier asking finance to change bank details, or a help-desk call asking to reset someone else’s MFA. Generative AI has made this harder to spot, with convincing writing and cloned voices; IBM names AI deepfake impersonation as a leading driver of AI-driven attacks in 2026.

How to fix it: verification procedures that do not rely on the caller (call back on a known number, require a second approver for payment changes), strict identity checks before help-desk resets, and training that uses current examples. Our guide to social engineering courses covers the defensive side in depth.

10. DoS and DDoS attacks

A denial-of-service (DoS) attack floods a website, server or network with more traffic or requests than it can handle, making it unavailable. A distributed denial-of-service (DDoS) attack does the same from many machines at once, usually a botnet of compromised computers and internet-of-things devices, which makes it far harder to block. The cost is downtime: lost sales, missed service levels and support load.

How to fix it: use a DDoS protection service or a content delivery network in front of public sites, set rate limits, keep spare capacity and have a runbook with your hosting or network provider.

11. Man-in-the-middle attacks

In a man-in-the-middle (MitM) attack, the attacker positions themselves between two parties, such as a user and a website, to read or alter traffic. Typical settings are rogue or unsecured public Wi-Fi, compromised routers and look-alike login pages that relay credentials in real time, a technique also used to get around weaker forms of MFA.

How to fix it: encrypt everything in transit (HTTPS/TLS everywhere, HSTS on your sites), use a VPN on untrusted networks, secure Wi-Fi with WPA3 or at least WPA2-Enterprise, and prefer phishing-resistant MFA, which checks the real site’s identity.

12. Insider threats

Not every threat comes from outside. Insider threats include malicious employees or contractors, but more often negligent ones: someone who emails a spreadsheet to a personal account, misconfigures a cloud storage bucket or keeps access after changing roles. Security practitioners on Reddit repeatedly named insiders and third-party suppliers as the threats that tools catch least.

How to fix it: least-privilege access reviewed regularly, prompt offboarding, data loss prevention for sensitive information, logging of access to critical systems, and a culture where reporting a mistake is safe.

How to identify network security threats

You cannot fix what you cannot see. Most organizations start with three layers of visibility:

• Asset and vulnerability management: an up-to-date inventory of devices and software, plus regular vulnerability scans checked against the KEV catalog.
• Logging and monitoring: central logs from firewalls, identity systems, endpoints and cloud services, reviewed by a SIEM or a managed detection service.
• Network traffic analysis: tools such as intrusion detection systems and packet analyzers (see our Wireshark tutorials) to spot unusual connections.

For small businesses without a security team, a managed service provider (MSP) or managed detection and response (MDR) service is usually the practical way to get this coverage, a point small-business owners on Reddit were advised again and again.

The security basics that stop most attacks

The same handful of controls appears in every major framework because it blocks most of the threats above:

• Patch quickly, starting with internet-facing systems and anything in the KEV catalog.
• Use MFA everywhere, phishing-resistant for admins and finance.
• Back up offline and test restores.
• Segment the network so one compromise cannot reach everything.
• Apply least privilege to users, admins and service accounts.
• Train people with short, regular, realistic exercises.
• Monitor and plan: central logging plus a written incident response plan.

Bolster access control measures

Access control decides who can reach what. Weak access control leaves the network open to unauthorized use, while strong access control limits the damage of every other threat on this page. Enforce strong, unique passwords through a password manager and a breached-password check, require multi-factor authentication wherever possible, remove standing admin rights in favor of just-in-time elevation, and review access when people change roles or leave.

Always install software updates & security patches

Software ships with flaws that are found and fixed later. A security update closes a door that attackers may already be trying, which is why exploited vulnerabilities now lead Verizon’s list of breach entry points. Keep a strict patch schedule, automate updates on endpoints, track end-of-life systems that no longer receive patches, and replace them.

Carry out proper employee training

Many breaches succeed because of one person’s honest mistake. Good security training is short, frequent and realistic: how to recognize phishing on email and phone, how to verify unusual requests, how to report something suspicious and who to contact. Measure it with simulated phishing and track reporting rates, not just click rates.

How to learn to defend against these threats

Network defense is a strong career path: the U.S. Bureau of Labor Statistics reports a 2025 median pay of $129,180 for information security analysts, with employment projected to grow 21% from 2025 to 2035, much faster than average. These are the best-supported starting points:

• Google Cybersecurity Professional Certificate (Coursera): 4.8 stars from 69,644 reviews, about six months at seven hours a week, no experience required; included in Coursera Plus ($239 a year, normally $399).
• CompTIA Security+ (SY0-701) Complete Course by Jason Dion (Udemy): 4.7 stars from 124,613 ratings, 31 hours, updated October 2026. Security+ is the standard entry-level security certification.
• CompTIA Security+ Certification Bootcamp (Zero To Mastery): a nine-hour beginner bootcamp aimed at passing Security+.
• Networking first: if TCP/IP, ports and routing are new to you, start with our computer networking courses and CompTIA Network+ training.

For more options, see our guides to cyber security courses, cybersecurity certifications and CompTIA Security+ training.

Start the Google Cybersecurity certificate →

Conclusion

No network is ever 100% secure, and attackers keep adapting; the 2026 reports show them shifting from tricking people toward exploiting systems and using AI to move faster. But the threats that cause most damage are well understood, and so are the defenses. Patch quickly, require strong MFA, keep offline backups, segment your network, limit access and train your people, and you will have closed the doors most attackers try first.

Frequently asked questions

What is the most common network security threat?

In 2026, exploited software vulnerabilities are the most common way into a network: Verizon’s 2026 Data Breach Investigations Report found 31% of breaches start that way, ahead of stolen credentials. Phishing and other social engineering remain very common, and ransomware appears in 48% of breaches.

What are the main types of network security threats?

The main types are malware (viruses, worms, trojans, spyware, rootkits and ransomware), social engineering (phishing, vishing, smishing and impersonation), exploited vulnerabilities, stolen or weak credentials, denial-of-service attacks, man-in-the-middle attacks and insider threats.

How do you prevent network security threats?

The fundamentals stop most attacks: patch quickly, use multi-factor authentication, keep offline backups, segment the network, apply least privilege, train users against phishing, and monitor for unusual activity with a written incident response plan.

How much does a data breach cost?

IBM’s Cost of a Data Breach Report 2026 puts the global average at $4.99 million, a 12% increase on the previous year and a record high, driven by higher detection, escalation and lost business costs.

What is the difference between a threat and a vulnerability?

A threat is something that could cause harm, such as ransomware or a phishing campaign. A vulnerability is the weakness it exploits, such as an unpatched server or a reused password. Risk combines the two: how likely an attack is and how much damage it would do.

What are network security threats and solutions for a small business?

Small businesses face the same top threats: phishing, ransomware, stolen passwords and unpatched systems. The most cost-effective solutions are MFA on email and cloud accounts, automatic updates, offline backups, endpoint protection and a managed service provider for monitoring.

How can I learn network security?

Start with networking fundamentals, then an entry-level security course such as the Google Cybersecurity Professional Certificate on Coursera or a CompTIA Security+ course. Security+ is the most common first certification for security roles.

Related reading: cyber security trends, hacking terminology explained, is ethical hacking legal?, mobile security testing tools, AI and cybersecurity and CCNA courses.