Backup and Restore MBR

Backing up Master Boot Record (MBR)
The MBR  is a 512 byte segment on the very first sector of your hard drive composed of three parts: 1) the boot code which is 446 bytes long, 2) the partiton table which is 64 btyes long, and 3) the boot code signature which is 2 bytes long. The core of the backup command is dd—which will be familiar to every system administrator, especially to those who intend to clone an entire hard disk. To see all the options type man dd. As we want to back up only the first 512 bytes we need to append some arguments to it. Here is the full command you need (and remember to run it as the root user, su (and sudo for Ubuntu users):

dd if=/dev/hda of=/home/richmondg/mbr_backup bs=512 count=1

Restoring the MBR

You can use a live CD to access your hard drive and read the backup off any removable media such as a USB stick. Here is the command:

dd if=/dev/sda/mbr_backup of=/dev/hda bs=512 count=1

Again, amend sda to read where you saved the MBR and run the command as root. If you wish to kill the MBR altogether, including the partition table, then you can overwrite it with a series of zeros:

dd if=/dev/zero of=/dev/hda bs=512 count=1

If you want to kill the MBR but leave the partition table intact then simply change 512 to 446.

Another way to repair the mbr of your HDD device is install LILO then type (replacing x with the letter of your HDDdevice) :

lilo -M /dev/sdx

Most commonly used Security Techniques against viruses.

Virus detection and its removal are mode through an antivirus or with some other security program. Different antivirus programs are available in the market and over Internet. The most common and famous security technique against viruses is as under: 

Virus Signature/ Virus Definition

Virus signature is a known pattern of code of a code of a virus program; this pattern is used by antivirus program to detect viruses and then to remove these viruses. You should update virus definition continuously by downloading updates from Internet. This ensures that your antivirus is always able to detect changing viruses. 

Inoculation

Inoculation file is separate file created and maintained by antivirus program to record information like file size and file creation date. This information later on is used for virus detection and removal.
 

Quarantine

Quarantine is a separate area on a hard disk. It contains the infected files and folders that cannot be cleared or deleted by antivirus due to some reason, for example sharing violation or unknown virus for that antivirus. 

Recovery Disk

Recovery disk is a removable disk that holds un-infected system commands and startup information. In case the boot record of actual hard disk fails, this recovery disk can be used to start the computer. Afterwards an antivirus program can be used to remove the virus. 

Un-authorized access

Accessing a computer system without the knowledge or permission of its user is called unauthorized access. It is always recommended to restrict computer resources with the help of usernames and passwords. These are unique combination of characters to identify users and their secret codes respectively. 

Firewall

Firewall is a security system consisting of hardware and software to prevent unauthorized access of a network or computer. Big companies use a separate computer firewall software or hardware to protect their date from unauthorized access. Firewall check outgoing and incoming traffic and manage data access to the authorized users only. 

Biometric Devices

A biometric device reads personal characteristics like fingerprints hand structure, facial features, and voice recognition to authenticate a user for any further access to a computer system or other peripheral devices. A biometric device translates the personal characteristics into digital code that is matched to already store user data in that system. If the digital data matches with any of the stored data, it gives access to the person. In case of no match, the access is denied.