Common types of computer viruses you need to watch out for

Here at Interpro Technology, we’ve encountered countless examples of how a single virus can wreak havoc on a company’s operations. From user education and endpoint security to constant vigilance, our years of experience have shown us one thing above all: understanding the landscape of computer viruses is crucial for anyone who wants to stay safe in today’s digital world.

In this article, we’ll walk you through the most prevalent types of viruses, delve into how they work, and share practical guidance on safeguarding your systems. We’ll also refer to insights from this helpful resource to give you an even broader understanding. So, let’s dive in and make sure you’re well-armed against these ever-evolving threats!

What Are Computer Viruses?

Computer viruses are a form of malicious software specifically designed to replicate themselves and spread from one system to another, much like a biological virus. Unlike some other kinds of malware that remain stationary, a virus usually requires a host file—often an executable program or a document with macro functionality—to latch onto. Once active, it can execute its payload, which might involve corrupting files, stealing data, or even making your machine practically unusable.

Key Characteristics

• Replication: Viruses can copy themselves into other programmes or files.
• Trigger: Many viruses are dormant until you open or run an infected file.
• Payload: This is a malicious act, ranging from minor nuisances (like displaying pop-up ads) to significant damage (e.g., deleting system files).
• Viruses are just one subset of malware threats. The broader term “malware” includes Trojan horses, spyware, adware, ransomware, worms, and more. Each operates differently, but understanding viruses is a crucial first step in building a solid cyber defence.

Why Understanding Viruses Matters

It’s easy to think, “Oh, I have antivirus software—surely that’s enough?” While virus protection programmes are indeed vital, they’re only one layer of your security arsenal. Viruses are constantly evolving, and new ones appear daily, often employing clever strategies to slip past traditional security measures.

Impacts on Businesses

• Downtime: Even a single infected machine can interrupt workflows, costing time and money.
• Reputational Damage: Clients might lose trust if they experience a large-scale breach.
• Financial Losses: From paying for data recovery or extended IT support to potential legal fees if customer data is compromised.

Effects on Individuals

• Identity Theft: Some viruses harvest personal information for fraudulent activities.
• Stolen Credentials: Keylogging or spyware elements can record login details or credit card data.
• System Instability: Slow performance, frequent crashes, or even total system failure.
• Real-world examples are rife, from high-profile ransomware attacks shutting down entire healthcare systems to malicious worms that spread through global networks in mere hours.
• Every story highlights the importance of vigilance, user education, and layered security.

Trojan Horses

Trojan horse viruses are among the most insidious because they disguise themselves as legitimate software or files. You might think you’re downloading a helpful utility, only to discover it harbours hidden code designed to compromise your system.

How Trojans Infiltrate Systems

• Phishing Emails: Malicious links or attachments appear genuine, luring you into downloading the Trojan.
• Rogue Applications: Software from unverified sources, such as sketchy websites or torrent platforms, can harbour Trojan installers.
• Social Engineering: Attackers craft messages to convince you the file is something you desperately need.

Consequences from Trojan Infiltrations

• Data Theft: Trojans can secretly siphon off login credentials, personal documents, or financial details.
• Remote Access: Some Trojans install backdoors, allowing cybercriminals to control your machine.
• Wider Infections: Once a Trojan is in, it can pave the way for additional malware.

Best Practices to Keep in Mind

• Keep your operating system updates current. This is key in the fight against Trojans!
• Use reputable antivirus or endpoint security solutions.
• Train staff to recognise phishing emails and suspicious attachments.

Worms

While a Trojan needs user interaction to trigger its payload, worm infections can spread all on their own. Worms exploit security weaknesses in networks, systems, or applications, replicating themselves at an alarming rate.

Common Vectors

• Unsecured Networks: Worms hop between machines sharing the same network.
• Outdated Software: Old, unpatched operating systems are a buffet for worms.
• Weak Passwords: Brute-force attempts can crack poorly secured network credentials.

Potential Damage

• Bandwidth Consumption: A rapidly spreading worm can clog network resources.
• File Corruption: Some worms carry malicious payloads, corrupting or deleting data.
• System Crashes: Overwhelmed systems might freeze or reboot endlessly.

Countermeasures

• Keep software patches up-to-date.
• Enforce strong password policies.
• Monitor network traffic for suspicious spikes.
• Use firewall protection to block unauthorised traffic.

Macro Viruses

Macro viruses take advantage of macros—scripts that automate tasks in software like Microsoft Word, Excel, or PowerPoint. These viruses often travel through seemingly innocent document attachments.

How Macro Viruses Spread

• Email Attachments: A malicious Word or Excel file might be sent to unsuspecting recipients.
• Shared Documents: If staff share files on a common drive, an infected macro can proliferate quickly.
• Enable Macros Prompt: Many programs ask if you want to enable macros. A single careless click can activate the virus (so double check what you are doing).

Warning Signs

• Unexpected prompts or pop-ups when opening documents.
• Strange file behaviour, like automatically saving, closing, or changing contents.
• Anti-virus alerts indicating macro-based threats.

Protective Measures

• Disable macros by default, enabling them only from trusted sources.
• Teach employees to be wary of opening unfamiliar documents.
• Keep Microsoft Office fully updated to benefit from the latest security patches.

Boot Sector Viruses

Some of the earliest malware threats were boot sector viruses, which target the boot sector of hard drives or other media like USB sticks. By infecting this crucial area, they load before the operating system even starts, making them particularly tricky to remove.

Consequences of Boot Viruses

• System Instability: If the boot sector is corrupted, your system might fail to start.
• Spread via External Media: Infected USB drives or CDs can propagate the virus to any computer they connect to.
• Historical Prevalence: While less common today, they still exist and can be devastating if they resurface on unprotected machines.

Defensive Actions You Can Take

• Use reputable antivirus software that scans boot sectors.
• Avoid using unknown external media without a thorough scan.
• Keep your BIOS or UEFI firmware updated if possible.

Polymorphic Viruses

A polymorphic virus morphs its code to evade detection. Traditional antivirus solutions, which often rely on matching known virus signatures, can struggle because the virus changes its signature each time it replicates.

Why They’re Challenging

• Constant Code Alterations: The virus rewrites itself, making it look different even though its function remains the same.
• Advanced Evasion Techniques: Some polymorphic viruses employ encryption or obfuscation.
• Rapid Propagation: Each new generation may spread quickly, making containment more difficult.

Battling Polymorphic Threats

• Use heuristic analysis and behaviour-based detection tools, which spot suspicious behaviour rather than known signatures.
• Keep all security software, from antivirus to firewalls, updated.
• Encourage users to report odd system behaviour immediately. If you’ve not got a system in place for this, reach out to our team.

Ransomware (Honourable Mention)

Technically, ransomware is classified under the umbrella of malware rather than a traditional virus, but it’s far too significant to ignore. This nasty threat encrypts files and demands payment (often in cryptocurrency) for release.

Methods of Infection

• Phishing Emails: Links or attachments loaded with malicious code.
• Malicious Adverts: Known as “malvertising,” these adverts can compromise your system just by visiting a webpage.
• Exploiting System Vulnerabilities: Out-of-date software is a prime target.

Best Practices to Prevent Ransomware

• Perform frequent backups and store them off-site or in the cloud.
• Teach staff to spot phishing attempts and suspicious links.
• Consider DNS filtering and advanced threat intelligence solutions.

Adware and Spyware

Adware and spyware might not always behave like a classic “virus,” but they can be just as detrimental.

Adware

• Displays Unwanted Ads: Often in the form of pop-ups or embedded banners.
• Tracks Online Activity: Companies or cyber criminals gather data to target you with more ads.
• System Slowdown: Multiple ads running in the background can tank performance.

Spyware

• Data Harvesting: Gathers sensitive details like browsing habits, usernames, and passwords.
• Stealth Operation: Often runs unnoticed, meaning victims remain unaware for extended periods.
• Can Include Virus Components: Some spyware also acts like a trojan, opening backdoors for further infections.

Removal and Prevention

• Use reputable adware removal and anti-spyware tools.
• Keep a close eye on new software installs—avoid “bundled” extras.
• Monitor for unusual network activity or data usage.

Keyloggers

One of the most alarming threats is a keylogger, which records every keystroke you make. This includes usernames, passwords, credit card numbers—essentially everything you type.

Infection Methods

• Bundled Malware: Keyloggers often come as part of a Trojan horse package.
• Physical Devices: Sometimes attackers plug a small piece of hardware between your keyboard and computer.
• Compromised Websites: Exploit kits on malicious sites can install software-based keyloggers.

Why They’re Dangerous

• Identity Theft: Straight access to login credentials, financial details, and personal information.
• Corporate Espionage: Sensitive business data can be siphoned off to competitors or criminals.
• Hard to Detect: Keyloggers usually run silently in the background.

Protective Steps

• Maintain a robust firewall and multi-factor authentication.
• Regularly scan your system for unusual processes.
• Inspect hardware connections if you suspect tampering.

Tell-Tale Signs Your System May Be Infected

A successful infection doesn’t always manifest with dramatic crashes. Sometimes, a virus can lurk for weeks without drawing attention. Here are some red flags:

• Sluggish Performance: If routine tasks or opening files feel excruciatingly slow, you might have a background virus.
• Unexpected Pop-Ups: Excessive adverts or alerts you never authorised can be a clue.
• Random Crashes or Freezes: Occasional glitches are normal, but repeated incidents could hint at deeper problems.
• Suspicious Network Activity: Keep an eye on your data usage—spikes might indicate a worm or other malicious traffic.
• Unauthorised Settings Changes: If your homepage, default search engine, or system configurations change spontaneously, be wary.

If you spot these warning signs, take immediate action: disconnect from the internet, run a reputable antivirus or endpoint security scan, and consider seeking professional help if the infection persists.

How to Protect Yourself and Your Organisation

Now that we’ve explored the myriad ways viruses can infiltrate your systems, let’s focus on practical strategies to prevent infections and minimise damage if one occurs.

• Regular Updates: Keep your operating system, web browsers, and software applications patched and up-to-date. These security patches fix vulnerabilities that viruses love to exploit.
• Robust Antivirus/Endpoint Security: Choose a reputable solution capable of real-time scanning and heuristic analysis. Set it to update virus signatures automatically, so you’re covered against the latest threats.
• Firewalls: Both hardware and software firewalls are essential. They are a barrier between your internal network and the outside world, filtering out suspicious traffic.
• User Education: People are often the weakest link. Train your team to recognise phishing emails, questionable links, and suspicious pop-ups. Encourage them to report anything out of the ordinary.
• Data Backups: Make frequent, secure backups of critical data. Ideally, keep these backups offline or in a protected cloud environment. A robust backup strategy can save you from catastrophic data loss if a virus or ransomware outbreak occurs.
• Incident Response Plan: Outline what to do if you suspect a virus infection, from isolating infected devices to notifying relevant stakeholders. Quick action can prevent a minor incident from evolving into a full-scale breach.
• Restrict Permissions: Grant the bare minimum access rights. This principle of “least privilege” reduces the chances of viruses spreading through shared folders or servers.
• Multi-Factor Authentication (MFA): If credentials are compromised through a keylogger or Trojan, MFA adds another layer of defence, making it harder for attackers to log in.

Computer viruses aren’t just a nuisance; they’re a genuine threat to both individual users and large-scale organisations. From file infector viruses embedding themselves into critical programmes to polymorphic malware morphing their signatures to dodge detection, the scope of malicious software seems almost limitless. Even tangential threats like ransomware, adware, and spyware pose serious risks that demand our full attention.

Yet, there’s good news: most infections can be avoided by practising a bit of caution and maintaining a layered security approach. Updating your software, scanning attachments, training your staff, and backing up data regularly all help build a fortress around your systems.

Remember, prevention is always better than cure! If you’re unsure about any aspect of virus protection—or want a helping hand in implementing top-notch security protocols—our friendly team at Interpro Technology is always here to guide you. Feel free to reach out and let us know how we can help bolster your digital defences. After all, a safer online environment benefits everyone.

Stay vigilant, stay informed, and stay secure!