Client and Network level Internet Security and Access Management :
Antivirus
AntiSpyware
Mail Spam
Network Firewall
Internet Content Filtering
Internet access Monitoring
Bandwidth Management, etc.
A computer virus is a self-replicating computer program written to alter the way a computer operates without the permission or knowledge of the user.
What are the effects of viruses?
The most benign viruses are merely annoying. The worst viruses destroy data
and ruin your operating system.
Some viruses infect existing files on your computer, transforming regular files (like Word documents or system files) into infected files. Other viruses delete certain types of files on your computer. Still others are little more than jokes, which display annoying messages or interfere with your mouse cursor, but are otherwise harmless.
How do viruses spread?
One thing all viruses have in common is that they spread. Viruses will often spread from one infected file to another on the same computer. Many viruses also attempt to infect other computers.
What are the effects of viruses?
The most benign viruses are merely annoying. The worst viruses destroy data
and ruin your operating system.
Some viruses infect existing files on your computer, transforming regular files (like Word documents or system files) into infected files. Other viruses delete certain types of files on your computer. Still others are little more than jokes, which display annoying messages or interfere with your mouse cursor, but are otherwise harmless.
How do viruses spread?
One thing all viruses have in common is that they spread. Viruses will often spread from one infected file to another on the same computer. Many viruses also attempt to infect other computers.
Email Viruses - A common tactic for a virus is to attach itself to outgoing email. An infected computer's address book can provide the virus with lots of email addresses to which it can send itself. You should avoid clicking on an email attachment you weren't expecting to receive, even if you know the sender.
Instant Messaging - Some viruses can use instant messaging programs like AOL Instant Messenger (AIM) to infect others. An instant message sent by a virus might say, "Check this out!" When your friend clicks the link, that person's computer is infected too. Be cautious about links sent to you in IM.
Shared Folders - Some viruses scan the network for unprotected shared folders. If your computer has a shared folder that's not password protected, it could be an open doorway for a virus. You should always make sure shared folders on your computer are protected.
System Vulnerabilities - Some viruses look for computers that have vulnerabilities. If a virus finds a vulnerable computer, it can exploit the machine to infect it. To protect your computer, you should always stay up to date with critical system updates for your operating system and web browser.
MBR: Master Boot Record
The master boot record is, in a sense, a small program that is automatically executed when the computer is booted. It resides in the hard drive's master boot sector which is located at the very beginning of the drive. The main function of the code contained within the MBR is to give the operating system valuable information about how the hard drive is organized. Since the MBR is accessed so early on in the boot process, it is an excellent target for viral infection. A boot sector virus will overwrite the MBR's code with its own code so that it is executed first. The virus will generally copy the actual MBR to another place on the hard drive and give control back to it after the virus gets a chance to execute.
Partition Table
The partition table is a small storehouse of information that tells the operating system where to look for its specific boot code. It is located in the master boot sector and is read by the master boot record at bootup. Thus, if you had both DOS and Linux installed on your hard drive, the partition table would contain the information pointing to the boot code of each of these operating systems. This information is often either moved, or encrypted by boot sector viruses.
Glossary
CMOS
The CMOS, complimentary Metal Oxide Semiconductor, is a small segment of internal memory which contains vital information about your entire computer: its number of drives, their size, amount of RAM, etc. Without the information contained in the CMOS your computer would be virtually useless. At the present time, only a handful of viruses, most notably exebug, will target the CMOS.
The CMOS, complimentary Metal Oxide Semiconductor, is a small segment of internal memory which contains vital information about your entire computer: its number of drives, their size, amount of RAM, etc. Without the information contained in the CMOS your computer would be virtually useless. At the present time, only a handful of viruses, most notably exebug, will target the CMOS.
Spyware
An Overview about spyware and how to protect against them:
http://www.helpdesk.ilstu.edu/kb/index.phtml?kbid=1150
An Overview about spyware and how to protect against them:
http://www.helpdesk.ilstu.edu/kb/index.phtml?kbid=1150
TSR
TSR stands for terminate, but stay resident. A TSR program will remain resident in your computer's memory after it executes. Programs such as memory managers, disk caching software, and device drivers reserve a section of your computer's memory so that they can continue to perform their function for the whole time your system is turned on. Many viruses, (particularly boot sector viruses), will stay resident in memory so they can spread to other disks and programs much faster and more transparently. In addition, once a virus becomes memory-resident it is much harder to detect because it can monitor every action taken by your computer and cover its tracks accordingly.
TSR stands for terminate, but stay resident. A TSR program will remain resident in your computer's memory after it executes. Programs such as memory managers, disk caching software, and device drivers reserve a section of your computer's memory so that they can continue to perform their function for the whole time your system is turned on. Many viruses, (particularly boot sector viruses), will stay resident in memory so they can spread to other disks and programs much faster and more transparently. In addition, once a virus becomes memory-resident it is much harder to detect because it can monitor every action taken by your computer and cover its tracks accordingly.
.exe file
A .exe file is the most common type of program in the PC world. Though they are not as compact as .com programs, they provide a great deal of functionality and flexibility in terms of what they can accomplish. Viruses that can infect .exe files generally have a better chance of surviving because there are more places in an .exe file for a virus to hide. All .exe files begin with a header that tells the program how large it is and how much memory it needs to allocate. After the header there is a blank space, usually about 512 bytes long, that contains nothing but blank characters. This space is a perfect place for a virus to hide itself. Since the virus is simply filling a blank space in the file, the size of the infected file does not change, making the infection much more inconspicuous.
A .exe file is the most common type of program in the PC world. Though they are not as compact as .com programs, they provide a great deal of functionality and flexibility in terms of what they can accomplish. Viruses that can infect .exe files generally have a better chance of surviving because there are more places in an .exe file for a virus to hide. All .exe files begin with a header that tells the program how large it is and how much memory it needs to allocate. After the header there is a blank space, usually about 512 bytes long, that contains nothing but blank characters. This space is a perfect place for a virus to hide itself. Since the virus is simply filling a blank space in the file, the size of the infected file does not change, making the infection much more inconspicuous.
.com file
A .com file is a program that ends with an extension of .com. The vast majority of PC-based viruses are .com programs. There are several reasons for this. The most important reasons are:
A .com file is a program that ends with an extension of .com. The vast majority of PC-based viruses are .com programs. There are several reasons for this. The most important reasons are:
Since .com programs contain instructions that can be executed by a computer without interpretation they tend to operate faster.
.com programs are much more compact than their .exe counterparts so they are easier to hide.
In DOS, except for internal commands, .com files will always execute before any other program of the same name with a different extension. For example, if you have three programs called chart.com, chart.exe, and chart.bat in the same directory, typing "chart" will execute chart.com. A special type of virus called a companion virus exploits this situation by searching for a file with an .exe extension and creating a hidden file of the same name with a .com extension containing a virus. Thus, typing a program's name will execute the virus first, (since it has a .com extension), then code contained within the virus will start the actual .exe program.