1. Types of Electronic Infection
1. Computer viruses
2. Worms
3. Trojan horses

2. 1.Computer virus 17.3 Electronic Infection
A program that attaches itself to a real program
Each time the user’s program runs, the virus runs too
Can corrupt a computer system
Can replicate itself to infect other computer systems

3. 1.Computer virus 17.3 Electronic Infection
spreading through messages
Spread via the Internet
Spread through storage media

4. 1.Computer virus: Spread through e-mail messages
17.3 Electronic Infection
virus
1.Computer virus:
Spread through messages
Most common way of virus transmission
Computers usually infected through attachments
Virus replicates itself by automatically mailing itself to people in victim’s address book

5. 1.Computer virus: Spread via the Internet 17.3 Electronic Infection
Source of viruses
Good practice to scan suspicious downloads

6. 1.Computer virus: Spread through Storage Media
17.3 Electronic Infection
1.Computer virus:
Spread through Storage Media
Storage Media: Floppy Disks, CD- ROM etc…
NOT the major sources for spreading computer viruses nowadays
Files in a disk may be infected with virus downloaded from the Internet or attached to s

7. 2.Worms Method of spreading 17.3 Electronic Infection
A computer program that uses computer networks and security loopholes to spread out and replicate itself.
Method of spreading
A copy of the worm scans the network for another machine with a specific security loophole
The worm copies itself to the new computer using the security loophole.

8. 3.Trojan Horses 17.3 Electronic Infection
A computer program that intends to perform malicious or destructive actions
Hide well or looks like real programs
Running these programs the Trojan horse enters without any notice
Hackers, with Trojan horses, can
Steal sensitive information such as passwords and credit card numbers
Remotely control the victim’s computer
NOT a virus as there is NO REPLICATION

9. Avoiding Virus Attacks
17.3 Electronic Infection
Avoiding Virus Attacks
1. Antivirus software
Examine files stored on disk or downloaded from the Internet
Determine whether they are infected
Disinfect the files if necessary
Scan for virus signatures to identify a known virus

10. Avoiding Virus Attacks
17.3 Electronic Infection
Avoiding Virus Attacks
2. Measures to prevent infection
Do not accept files from high-risk sources
Install updated antivirus software
Update virus signatures regularly
Scan computer at regular intervals to ensure that it is free from virus
Scan all incoming files before opening
Backup programs and data regularly
Change passwords at regular intervals

11. 1. What is an Encryption? 17.4 Securing Internet Transaction
The process of converting readable data (plaintext) into unreadable characters (ciphertext)
Can prevent unauthorized access
Read the encrypted file → Decryption → Readable form
The reverse process is called decryption
The encryption process generally requires
-Algorithm
-A mathematical formula
-Encryption key
-A string of numbers and characters

12. 2. Symmetric Key Encryption & Public Key Encryption
17.4 Securing Internet Transaction
2. Symmetric Key Encryption
& Public Key Encryption
Symmetric Key Encryption
BOTH the sender and the recipient use the SAME key to encrypt and decrypt data
Problem
Need one key for each partner → problem of key management and storage when a lot of people need to communicate

13. 2. Symmetric Key Encryption & Public Key Encryption
17.4 Securing Internet Transaction
2. Symmetric Key Encryption &
Public Key Encryption
Public Key Encryption
Two keys (Public Key & Private Key)
Public Key
Used for encryption
Known to every person and placed on a public-key server
Private Key
Used for decryption
Should be kept confidential

14. 3. Digital Certificate 17.4 Securing Internet Transaction
Guarantees the identity of a user involved in a transaction
Also called a public-key certificate
Issued and verified by a certificate authority (CA)
Typically contains
Holder’s name
Holder’s public key
Expiration date
Issuing CA’s name and signature
Serial number of certificate

15. 4. Secure Sockets Layer (SSL)
17.4 Securing Internet Transaction
4. Secure Sockets Layer (SSL)
A protocol that provides secure data transmission between web servers and browser
A web site providing SSL must have a digital certificate
Web sites use them to transmit confidential information like passwords and credit card numbers
Web pages that use SSL typically begin with instead of

16. 4. Secure Sockets Layer (SSL)
17.4 Securing Internet Transaction
4. Secure Sockets Layer (SSL)

17. 5. Securing E-mail Messages
17.4 Securing Internet Transaction
5. Securing Messages
An message passes through a number of servers before reaching the recipient.
Messages can be read by everyone if pried intentionally.
Messages containing confidential information should be encrypted before being sent.

18. 6. Digital Signature 17.4 Securing Internet Transaction
A digital code attached to a message
Used to identify the sender and verify that the received message has not been altered during transmission
Generation process of digital signatures relies on public key method