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How does anti-virus software work?
Posted On 24/12/2009 12:37:50
How does anti-virus software work?

An anti-virus software program is a computer program that can be used to scan files to identify and eliminate computer viruses and other malicious software (malware).

Anti-virus software typically uses two different techniques to accomplish this:

  • Examining files to look for known viruses by means of a virus dictionary
  • Identifying suspicious behavior from any computer program which might indicate infection

Most commercial anti-virus software uses both of these approaches, with an emphasis on the virus dictionary approach.

Virus dictionary approach
In the virus dictionary approach, when the anti-virus software examines a file, it refers to a dictionary of known viruses that have been identified by the author of the anti-virus software. If a piece of code in the file matches any virus identified in the dictionary, then the anti-virus software can then either delete the file, quarantine it so that the file is inaccessible to other programs and its virus is unable to spread, or attempt to repair the file by removing the virus itself from the file.

To be successful in the medium and long term, the virus dictionary approach requires periodic online downloads of updated virus dictionary entries. As new viruses are identified "in the wild", civically minded and technically inclined users can send their infected files to the authors of anti-virus software, who then include information about the new viruses in their dictionaries.

Dictionary-based anti-virus software typically examines files when the computer's operating system creates, opens, and closes them; and when the files are e-mailed. In this way, a known virus can be detected immediately upon receipt. The software can also typically be scheduled to examine all files on the user's hard disk on a regular basis.

Although the dictionary approach is considered effective, virus authors have tried to stay a step ahead of such software by writing "polymorphic viruses", which encrypt parts of themselves or otherwise modify themselves as a method of disguise, so as to not match the virus's signature in the dictionary.

Suspicious behavior approach
The suspicious behavior approach, by contrast, doesn't attempt to identify known viruses, but instead monitors the behavior of all programs. If one program tries to write data to an executable program, for example, this is flagged as suspicious behavior and the user is alerted to this, and asked what to do.

Unlike the dictionary approach, the suspicious behavior approach therefore provides protection against brand-new viruses that do not yet exist in any virus dictionaries. However, it also sounds a large number of false positives, and users probably become desensitized to all the warnings. If the user clicks "Accept" on every such warning, then the anti-virus software is obviously useless to that user. This problem has especially been made worse over the past 7 years, since many more nonmalicious program designs chose to modify other .exes without regards to this false positive issue. Thus, most modern anti virus software uses this technique less and less.

Other ways to detect viruses
Some antivirus-software will try to emulate the beginning of the code of each new executable that is being executed before transferring control to the executable. If the program seems to be using self-modifying code or otherwise appears as a virus (it immeadeatly tries to find other executables), one could assume that the executable has been infected with a virus. However, this method results in a lot of false positives.

Yet another detection method is using a sandbox. A sandbox emulates the operating system and runs the executable in this simulation. After the program has terminated, the sandbox is analysed for changes which might indicate a virus. Because of performance issues this type of detection is normally only performed during on-demand scans.

Issues of concern

Macro viruses, arguably the most destructive and widespread computer viruses, could be prevented far more inexpensively and effectively, and without the need of all users to buy anti-virus software, if Microsoft would fix security flaws in Microsoft Outlook and Microsoft Office related to the execution of downloaded code and to the ability of document macros to spread and wreak havoc.

User education is as important as anti-virus software; simply training users in safe computing practices, such as not downloading and executing unknown programs from the Internet, would slow the spread of viruses, without the need of anti-virus software.

Computer users should not always run with administrator access to their own machine. If they would simply run in user mode then some types of viruses would not be able to spread.

The dictionary approach to detecting viruses is often insufficient due to the continual creation of new viruses, yet the suspicious behavior approach is ineffective due to the false positive problem; hence, the current understanding of anti-virus software will never conquer computer viruses.

There are various methods of encrypting and packing malicious software which will make even well-known viruses undetectable to anti-virus software. Detecting these "camouflaged" viruses requires a powerful unpacking engine, which can decrypt the files before examining them. Unfortunately, many popular anti-virus programs do not have this and thus are often unable to detect encrypted viruses.

Companies that sell anti-virus software seem to have a financial incentive for viruses to be written and to spread, and for the public to panic over the threat.


How to Format a Hard Drive With Windows XP
Posted On 22/12/2009 01:58:37

How to Format a Hard Drive With Windows XP

If you want to format a hard drive while using or installing Windows XP, you've come to the right place. This can be very useful for clearing everything off a secondary drive or when installing a fresh copy of Windows. Formatting a computer hard drive is simple and can help eliminate viruses, storage issues and other hard-to-resolve problems.

Preparation

1. When you format a computer hard drive you will lose everything that is on the drive. Therefore, it is very important to back up anything you might want later. Additionally, if you are going to be formatting and installing XP you need to make sure you have the discs for any applications or third party hardware you use since you will need to re-install your programs and drivers after re-installing Windows.

2. Take a moment to think of anything that you have on the computer that you wouldn't want to lose. Generally, you probably want everything in your My Documents folder, and you also want to save things like your favorites or bookmarks from your Web browser. Remember that each user on the computer has his or her own My Documents folder, Desktop items and Favorites/Bookmarks.

3. Save everything to a CD, DVD or a hard drive that you won't be formatting.

Formatting a Secondary Hard Drive

1. Right-Click on the “My Computer” icon either on your desktop or in the Start Menu and select “Manage.”

2. A new window titled “Computer Management” comes up. Select “Storage” from the left hand side by clicking it once, then select “Disk Management(local)” from the right side by double-clicking it.

3. Now in the lower part of the main frame (right side) of the window you should see a nice visual of all your hard drives. Each line is a different drive. Each box on a line (with a colored bar at the top and a size displayed in MB or GB) is a partition on the drive. Partitions are separations of space on a drive. Unless you are doing something specific that requires multiple partitions, you only want one partition per drive.

4. First you must delete any existing partitions on the drive you are going to format. Do this by right-clicking on the partition's box and selecting “Delete Partition...” Since you already know that you will be deleting everything on the drive, and have already backed everything up, you can safely say yes to any warning the computer presents you with.

5. If there are multiple partitions make sure you have saved everything off them since they might each have different drive letters (i.e. “D:” or “F:”). Then repeat the above step for each of them. If you only want to format one partition that is OK and you can continue to the next step without deleting the other partitions.

6. The box for the drive to be formatted should now have a black bar at the top of it and should say “Unallocated” under its size (see picture). Right click on it and select “New Partition...” The New Partition Wizard comes up.

7. In the New Partition Wizard click next. On the next page make sure “Primary Partition” is selected and click next. Now make the size equal to the maximum (it should already be set to it), and click next again. On the next page the computer will automatically choose the first available drive letter for the new drive. However, if you like you can choose another drive letter from the drop-down menu, and then click next.

8. Finally the New Partition Wizard asks if you would like to format the new partition and if so what format. Choose “NTFS” as it is faster and more secure. Leave the “Allocation unit size” as “Default.” In the “Volume label” field enter whatever name you want the drive to have. Simple is better. Avoid using spaces. Lastly, if the drive is brand new and has never been used before check the “Perform a quick format” box. If the drive has been used before leave this box unchecked. Leave the “Enable file and folder compression” box unchecked and click next. Then on the next page click finish.

9. The wizard will now spend a little while formatting the drive. On old or large drives this may take a while. Do not close the “Computer Management” window until it finishes. You will know it is done when the word under the size of the drive changes from “Formatting” to “Healthy” and the name and drive letter you chose for the new drive show up. After it is finished you can proceed to use your newly formatted drive.

Formatting and Installing from the Windows XP CD

1. This section explains how to reformat a drive from the Windows XP installation CD. This can be used when installing a fresh copy of Windows onto a computer. Here it is especially important to backup all of your important information because upon formatting you will lose EVERYTHING that used to be on the drive. This includes all applications and device drivers, so you must back up everything you can.

2. Insert your Windows XP installation disc into your CD drive (Home or Pro--it does not matter).

3. Now as you computer boots a little more it will say “Press any key to boot from CD..” press a key to do so.

4. The CD will load up a blue screen and then spend a while loading files it needs. When it is finished it will list a few options, mainly “Press ENTER to set up Windows XP.” Press Enter or Return.

5. Now you will be at a screen to select where to install Windows to. This is where you can delete old partitions and format drives. The box in the bottom half of the screen shows all your drives and the partitions that exist on them. Use the Up and Down arrow keys to highlight your “C:” partition and press the 'D' key (if all that shows up is “Unpartitioned space” and you have no C: or D: partitions, skip this step). On the next screen press the 'L' key to finalize deleting the partition.

6. Now you are back on the screen to choose where to install Windows. The box on the lower half of the screen should no longer show a partition but simply have an entry “Unpartitioned space xxxxxMB.” Select this with the arrow keys and press the 'C' key to create a partition on the drive. The next screen tells you the minimum and maximum sizes the partition can be and lets you pick the size. The default size is the maximum, but double check that the number entered is the maximum and hit enter.

7. Now you will again be back at the choose where to install Windows screen. But this time you will have a partition that looks something like this “C: Partition1 [New (Raw)]xxxxxxMB.” Highlight this entry and press enter.

8. The next screen lets you choose which file system to format the drive with. Choose NTFS as it is faster and more secure. If the drive is brand new and has never been used before then use one of the options that ends in “(Quick).” Or, choose one of the lower down options. Use the arrow keys to select the proper one and press Enter or Return.

9. From here you are all set and the installation of Windows will proceed starting with a format of your drive. This will take a while (over half an hour) so you can take a little break.