(i) Spam: Distribute unwanted e-mail to a large number of internet users.
(ii) Fraud: Manipulating data, for example changing the banking records to transfer money to an unauthorized account.
(iii) Cyber stalking: Harassing through online.
(iv) Spoofing: It is a malicious practice in which communication is send from unknown source disguised as a source known to the receiver.
(v) Virus: A virus is a small piece of computer code that can repeat itself and spreads from one computer to another by attaching itself to another computer file. One ofthe most common virus is Trojan.
(vi) Worms: Worms are self- repeating and do not require a computer program to attach themselves. Worms continually look for vulnerabilities and report back to the author of the worm when weaknesses are discovered.

Digital signature:
(i) Digital signatures are based on asymmetric cryptography and can provide assurances of evidence to origin, identity and status of an electronic document, transaction or message, as well as acknowledging informed by the signer.
(ii) To create a digital signature, signing software (email) Creates a one-way hash of the electronic data to be signed.
(iii) The user's private key to encrypt the hash, returning a value that is unique to the hashed data. The encrypted hash, along with other information such as the hashing algorithm, forms the digital signature. Any change in the data, even to a single bit, results in a different hash value.

(iv) This attribute enables others to validate the integrity of the data by using the signer's public key to decrypt the hash. If the decrypted hash matches a second computed hash of the same data, it proves that the data hasn't changed since it was signed.
(v) If the two hashes don't match, the data has either been tampered with in some way (indicating a failure of integrity) or the signature-was created with a private key that doesn't correspond to the public key presented by the signer (indicating a failure of authentication).

Types of Encryption :
There are two types of encryption schemes as listed below: Symmetric Key encryption, Public Key encryption.
(i) Symmetric Key Encryption:
Symmetric encryption is a technique to use the same key for both encryption and decryption. The main disadvantage of the symmetric key encryption is that all authorized persons involved, have to exchange the key used to encrypt the data before they can decrypt it. If anybody intercepts-the key information, they may read all message. Depicts the working of symmetric key encryption.
(ii) Public Key Encryption:
Public key encryption is also called Asymmetric encryption. It uses the concept of a key value pair, a different key is used for the encryption and decryption process. One of the keys is typically known as the private key and the other is known as the public key. The private key is kept secret by the owner and the public key is either shared amongst authorized recipients or made available to the public at large. The data encrypted with the recipient's public key can only be decrypted with the corresponding private key. public key encryption

Web sites typically use cookies for the following reasons :
(i) To collect demographic information about who has visited the Web site.
(ii) Sites often use this information to track how often visitors come to the site and how long they remain on the site.
(iii) It helps to personalize the user's experience on the Web site.
(iv) Cookies can help store personal information about users so that when a user subsequently returns to the site, a more personalized experience is provided.

(i) Social engineering:
A misuse of an individual's weakness, achieved by making them to click malicious links, or by physically accessing the computer through tricks. Phishing and pharming are examples of social engineering.
(ii) Phishing:
Phishing is a type of computer crime used to attack, steal user data, including login name, password and credit card numbers. It occurs when an attacker targets a victim into opening an e-mailor an instant text message. The attacker uses p .shing to distribute malicious links or attachments that can perform a variety of functions. including the extraction of sensitive login credentials from victims.
(iii) Pharming:
Pharming is a scamming practice in which malicious code is installed on a personal computer or server, misdirecting users to fraudulent web sites without their knowledge or permission. Pharming has been called "phishing without a trap": It is another way hackers attempt to manipulate users en the Internet. It -is a cyber-attack intended to redirect a website's traffic to a fake site.