39.1 What Is Malware – Types for Defenders
Quick answer: the short, self-contained version of this lesson is the guide What Is Malware? Types and How to Protect Yourself.
Malware = software designed to harm, spy, encrypt, or control systems without honest user intent. Types (Blue vocabulary):
| Type | Simple idea | Blue focus |
|---|---|---|
| Virus | Needs a host file; spreads when that file runs / is shared | Scan files; block autorun; least privilege |
| Worm | Self-spreads over network (often no user click) | Patch, segment, block lateral SMB/RDP |
| Trojan | Looks useful; hides payload (fake tool, cracked installer) | Reputation, allowlisting, signed software |
| Ransomware | Encrypts / locks; demands payment | Backups, EDR, least privilege, isolate |
| Spyware | Steals keystrokes, cookies, files | EDR, MFA, browser hardening |
| Adware | Aggressive ads / unwanted PUPs | Browser hygiene; remove PUPs |
| Rootkit | Hides itself / other malware deep in OS | Boot integrity, offline scan, reimage |
| Botnet | Many infected hosts obey a C2 (command and control) | DNS/egress filter; sinkhole; patch |
| Fileless | Lives in memory / scripts / legitimate tools (LOLBins) | Script logging, AMSI, EDR behaviour |
| Wiper | Destroys data (sometimes disguised as ransomware) | Offline backups; immutable copies; IR drills |
Thodkyaat: naav kam, behaviour jast – encrypt karto ka? Lateral jato ka? C2 boltoy ka? Samjla ka?
| Red team (attacker) does | Blue team (defender) detects / stops |
|---|---|
| Delivers trojanised "free tool" / cracked installer | Block untrusted downloads; SmartScreen / reputation; allowlisting |
| Uses worm-style lateral after foothold | Network segmentation; patch critical SMB/RDP bugs; EDR lateral alerts |
| Prefers fileless PowerShell / WMI to dodge old AV | Script block logging; AMSI; EDR behaviour rules; Constrained Language Mode where fit |
Ravindra Bagale's Tip
Students say "virus = all malware". Be precise in interviews: a virus infects a host file, a worm spreads by itself, a trojan pretends to be useful, ransomware encrypts and extorts. Exact definitions > scary stories. Remember this.
Ravindra Bagale's Tip – मराठी
Students "virus = सगळे malware" म्हणतात. Interview मध्ये clear बोला: virus host file ला, worm स्वतः पसरतो, trojan उपयोगी असल्याचे भासवतो, ransomware encrypt/extort. Exact definition > भीतीदायक गोष्टी. हे लक्षात ठेवा.
Ravindra Bagale's Tip – हिंदी
Students कहते हैं "virus = सारा malware". Interview में clear बोलो: virus host file को, worm खुद फैलता है, trojan उपयोगी होने का दिखावा करता है, ransomware encrypt/extort. Exact definition > डरावनी कहानियाँ. यह याद रखो.
Lab
Notes madhe 10-row table: type | one-line def | one Blue control. Fictional Sahyadri Traders Pune – Shraddha Bagale (accounts) cracked "PDF merger" install keli. Kontya type chi suspicion? 5 sentences liha (trojan / PUP path).
Real incident: WannaCry (2017)
WannaCry was a worm-like ransomware outbreak that spread widely using a Windows SMB vulnerability (EternalBlue-class). Public reporting (national CERTs, Microsoft, major outlets) stressed unpatched systems and rapid east-west spread. Defence theme: timely patching, network segmentation, disable unused SMBv1, backups that ransomware cannot reach. Source: Microsoft security response and CERT advisories (verify current pages).
Extended teaching notes
Why this lesson matters
Malware analysis in this course is defensive: recognise indicators, isolate hosts, preserve evidence. Never run unknown malware on your main OS or on someone else's network.
- Isolate the host from the network.
- Capture volatile data if trained to do so.
- Hash samples; search only in licensed/safe tools.
- Rebuild from a known-good image when unsure.
- Share IOCs with your SOC, not on random chats.
Mini case study
Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.
Defender's worksheet (do this today)
- Write the lesson title, date and the exact lab target you are allowed to use.
- List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
- Run one safe check from the lesson on a lab system only. Paste the command and output.
- Write a two-sentence fix you would give a teammate.
- Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.
Indian workplace (sample data)
Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).
Global practice
Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.
Everyday analogy
Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.
Key terms
- Control: a safeguard (patch, config, process, detection).
- Finding: a weakness backed by evidence.
- Remediation: the fix plus how you verified it.
- Scope: systems you have written permission to touch.
- Least privilege: only the access the task needs.
- Defence in depth: several layers so one failure does not end the story.
Common mistakes
- Skipping written permission "just for a quick scan".
- Practising on hostel, office or public targets without authorisation.
- Collecting tool output without writing the fix.
- Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
- Publishing screenshots that contain secrets, cookies or internal hostnames.
Recap
- Evidence, fix, owner, date.
- Own lab only.
- Fix > spectacle.