There are approximately 30,000 hacker-oriented websites that disclose hacker know-how and tips on how to create computer viruses or “bugs.” One virus, the Manila-generated “Love Bug,” virtually circumnavigated the globe in twelve hours, illustrating that a teenager with Internet access in an underdeveloped nation can wreak as much cyberspace havoc as a privileged teenager in a developed nation.

Computer N/w Infrastructure Weakness and Vulnerabilities

The regular 3-way TCP\IP Handshake has been depicted below:
1. Client---------SYN Packet-------------Host
2. Host-----------SYN\ACK Packet--------Clien
3. Client----------ACK Packet---------------Host
The Three way handshake established the trust relationship between the client and the host.

IP Spoofing
Spoofing is the creation of TCP/IP packets using somebody else's IP address. Routers use the "destination IP" address in order to forward packets through the Internet, but ignore the "source IP" address. That address is only used by the destination machine when it responds back to the source.

TCP SYN ATTACK
Also known as ‘Half Open Scanning’ because only half of the complete 3-way TCP\IP connection is established.
Client-----SYN Packet--- Host
Case I: (Open) Host-----SYN\ACK Packet-- Client
Case 2: (Closed) Host----RST\ACK Packet---- Client

In this attack the client continually sends and receives the ACK packets but it does not open the session. The server holds these sessions open, awaiting the final packet in the sequence. This cause the server to fill up the available connections and denies any requesting clients access.

TCP Sequence Number Attack
This is when the attacker takes control of one end of a TCP session. The goal of this attack is to kick the attacked end of the network for the duration of the session. Only then will the attack be successful. Each time a TCP message is sent the client or the server generates a sequence number. The attacker intercepts and then responds with a sequence number similar to the one used in the original session. This attack can then hijack or disrupt a session. If a valid sequence number is guessed the attacker can place himself between the client and the server. The attacker gains the connection and the data from the legitimate system. The only defense of such an attack is to know that it’s occurring

Distributed Denial of Service Attacks (DDoS)

A distributed denial of service attack (DDOS) is one in which an attacker first compromises a number of hosts, and installs a daemon on those hosts. At a later point, the attacker sends a request to the daemon on the compromised hosts asking it to begin flooding a target host with various types of packets.

Ping of Death Attack
Ø The maximum packet size allowed to be transmitted by TCP\IP on a network is 65 536 bytes.
Ø In the Ping of Death Attack, a packet having a size greater than this maximum size allowed by TCP\IP is sent to the target system.
Ø As soon as the target system receives a packet exceeding the allowable size, then it crashes, reboots or hangs.
Ø This attack can easily be executed by the ‘ping’ command as follows:
ping -l 65540 hostname

Smurf Attacks
1. In SMURF Attacks, a huge number of Ping Requests are sent to the Target system, using Spoofed IP Addresses from within the target network.
2. Due to infinite loops thus generated and due to the large number of Ping Requests, the target system will crash, restart or hang up.

Tear Drop Attack
Data sent from the source to the destination system, is broken down into smaller fragments at the source system and then reassembled into larger chunks at the destination system.
For Example:
Say data of 4000 bytes is to be sent across a network, then it is broken down into three chunks:
CHUNK A contains Bytes 1 to 1500.
CHUNK B contains Bytes 1501 to 3000
CHUNK C contains Bytes 3001 to 4000
1. In this example the range of CHUNK A is 1 to 1500, range of CHUNK B is 1501 to 3000 while the range of CHUNK C is 3001 to 4000.
2. However, in case of a Teardrop attack, these ranges of data chunks are overlapping. For Example, in case of a Teardrop attack, the same 4000 bytes would be broken down into the below three chunks:
CHUNK A contains Bytes 1 to 1500.
CHUNK B contains Bytes 1499 to 3000
CHUNK C contains Bytes 2999 to 4000
3. In this example the range of CHUNK A is 1 to 1500; range of CHUNK B is 1499 to 3000 while the range of CHUNK C is 2999 to 4000. Thus, the ranges are overlapping.
4. Since here the ranges are overlapping, the target system gets DOS!!!

Windows NT Registry Threats
Common NT Registry attacks include the L0pht Crack, the Chargen Attack, the SSPing/ JOLT, and the Red Button.