Lecture 10: Malware

Question 1

List some techniques used for propagation of malware

Answer 1

• Virus
• Trojan horse
• Worm
• Backdoor
• Attack kit
• Auto-rooter
• Downloader

Question 2

List some techniques used as payloads in malware

Answer 2

• Adware
• Flooders
• Keyloggers, Spyware
• Zombie, bomb
• Logic bomb
• Ransomware
• Rootkit
• Spammers

Question 3

Explain what a “Worm” is, and how it works

Answer 3

• Replicating program that propagates over net
  o Using email, remote exec, SW flaw (USB stick)
  o Zero-day exploit
  o Old bugs (NSA Leakage, Server Message Block (SMB), etc.)
• Has phases:
  o Does not damage the system immediately
  o Propagation phase: searches for other systems, connects to it, copies self to it and runs

Question 4

Explain what a “Virus” is, and how it works

Answer 4

• Piece of software that infects programs
  o Modifying them to include a copy of the virus
  o So, it executes secretly when host program is run

Question 5

List the four phases of a typical “Virus”

Answer 5

-	A typical virus goes through phases of:
o	Dormant
o	Propagation
o	Triggering
o	Execution

Question 6

List the four components of a typical “virus”

Answer 6

o Infection mechanism – enables replication
o Modification engine – for disguise
o Trigger – event that makes payload activate
o Payload – what it does, malicious or benign

Question 7

List some techniques a virus can use in order to hide itself

Answer 7

• Naïve (simply self replicating)
• Compress parts of self to hide size
• Encryption
• Polymorphism

Question 8

Explain how a “Naïve (simply self replicating) virus” can easily be found by virus protection software

Answer 8

A Naïve (simply self-replicating) virus can be detected by changing file size of infected programs

Question 9

Explain how a (partially) compressed “virus” can be found by virus protection software

Answer 9

• Detection can be done through inspecting contents of potentially infected programs,
• Checking the signature of potentially infected programs, or
• Examining if a program contains the fixed code V of a virus

Question 10

Explain how “Encrypted viruses” work

Answer 10

o	Generate key
o	Encrypt virus body
o	Copy
♣	The bootstrap (decryption engine with key), and
♣	The encrypted virus body
o	When start
♣	Decrypt the virus body
♣	Execute

Question 11

Explain how an “Encrypted Virus” can be found by virus protection software

Answer 11

We can look for program signature, and inspect if contents of program has changed

Question 12

Briefly explain how “Polymorphic viruses” work

Answer 12

o Rebuild the whole virus at every infection to something functionally identical
♣ Either add non-functional code, or
♣ Re-order instructions

Question 13

Briefly explain how a “Polymorphic Virus” can be found by virus protection software

Answer 13

o Focus on the decryption engine

Question 14

Explain what a “Macro Virus” is, how it works, and some of its strengths

Answer 14

•	Exploit macro/scripting capability of apps
o	Basic, Elisp, Javascript, …
•	Why:
o	Platform independent
o	Infects documents
o	Is easily spread

Question 15

Give an example of an “E-mail Virus”, and how it works

Answer 15

•	E.g. Melissa
o	Exploits MS Word Macro in attached doc
o	If attachment opened, macro activates
o	Sends email to all users in the address-book, and 
o	does local damage

Question 16

Explain what a “Trojan Horse” is, and how it works

Answer 16

• Based on social engineering
• It’s a program with two purposes, one obvious and one hidden from the user
• Today it’s often used to install other software or backdoors
• Trojan horses can be built
  o From existing programs using a special wrapper
  o Or designed from the start to be one

Question 17

Give some examples of “Integrity-loss”, and some causes for it

Answer 17

• Deletion of files, contacts, etc.
• Used in ransomware, to:
  o Encrypt files
  o Delete files
  o Collect ransom money (e.g. bitcoin)

Question 18

Give some examples of “Availability-loss”

Answer 18

• Deletion of files, change of firewall rules

- Physical integrity

Question 19

Explain what a “Logic-Bomb” is, and how it works

Answer 19

• A small bit of code that triggers on a specific condition
• Typically with malicious results
• No vector for spreading
• Installed directly
• Example: Disgruntled ex. employee plants a piece of code that at a given date will attempt to wipe out all company servers

Question 20

Explain what a “Bot” is, and how it works

Answer 20

• Program taking over other computers
• To launch hard to trace attacks
• If coordinated from a botnet, characteristics:
  o Remote control facility
  o Multi-layered network of bots

Question 21

Give some examples of possible uses for “Bots”

Answer 21

o	DDoS
o	Spamming
o	Manipulating on-line surveys
o	For using computational resources
♣	E.g. bit coin mining, password brute forcing
o	Cheating ad-providers
o	Spreading new malware

Question 22

Give some examples of “Confidentiality-loss”

Answer 22

-	Key loggers/pin loggers
o	Password theft
-	Spyware
o	Camera
o	Documents
-	Phishing 
-	Espionage
-	Identity theft

Question 23

Explain what “Backdoors” are, and how they work

Answer 23

• Software that gives access to a system
• Bypassing OS-login restrictions
• Often installed for legitimate reasons
• Only to later be abused

Question 24

Explain what “Rootkits” are, and how they work

Answer 24

• Program installed for admin access
• Malicious and stealthy changes to OS
• May hide its existence
  o Subverting report mechanisms on processes, files, registry entries etc.
• User or kernel mode
• Installed by Trojan or worm

Question 25

List some examples of countermeasures against malware

Answer 25

• Code signing
• Prevention/detection systems
• Generic Decryption

Question 26

Explain how “Code Signing” works

Answer 26

•	Used in digital SW distribution
•	Used by HW vendors to prevent execution of arbitrary SW
•	Used by OSes to install binary drivers
•	SW shipped with a digital certificate
•	Root of trust
o	HW checks signature of OS
o	OS checks signature of apps
o	App checks signature of plug-ins
o	…

Question 27

Give some examples of Malware “Prevention/detection systems”

Answer 27

• At network level
o E.g. to temporarily prevent a worm infection due to a known bug
• At application level
o E.g. SMTP servers inspecting mails
• Behavioral based
o E.g. it is unusual to attempt and fail several TCP connections
o E.g. An application that uses more CPU cycles than usual
• Honeypots
o Networked and local

Question 28

List identifying features for each of the “four generations” of Anti virus

Answer 28

o First – signatures scanners
o Second – heuristics
o Third – identify actions
o Fourth – combination packages

Question 29

Explain what “Generic Decryption” is, and how it works

Answer 29

• Run executable files through GD scanner:
  o CPU emulator
  o Virus scanner to check known virus signatures
• Let virus decrypt itself in interpreter
• Periodically scan for virus signatures
• Issue: is long to interpret and scan
  o Trade-off change of detection vs. time delay