Definition of Virus:
A Virus is a small program that embeds itself into other programs. When those other programs are executed, the virus is also executed, and attempts to copy itself into more programs. In this way, it spreads in a manner similar to a biological virus. viruses, by definition, can "infect" any executable code. Accordingly, they are found on floppy and hard disk boot sectors, executable programs, macro languages and executable electronic mail attachments.viruses can be found using a Virus Scanner or a Virus Wall. Some software products are also available to remove them with a minimum of harm to the "infected" files.
Some viruses are self-modifying, in order to make detection more difficult. Such viruses are called polymorphic (many shapes).
What are viruses
Computer viruses are small programs with the capability to replicate themselves - generally without a user's knowledge. For example such programs may write themselves onto every floppy disk used, or mail themselves to people in an address book.
Viruses usually also perform a secondary action - the 'payload'. These actions range from the purely annoying — such as repeatedly putting a message on your screen — to the very damaging — for example deleting or corrupting files, denying access to files or changing system settings. Occasionally this payload is set to trigger on a specific date. If this is the case then there will be no obvious sign of the infection.
Since a virus is a program, it needs to be executed to be a threat. A virus usually disguises itself or hides within another file, so as to trick a user into running it. Typically a virus arrives as part of an email attachment, though it may spread in other ways.
How viruses spread
The University has virus filtering and protection on its e-mail and file servers and also blocks certain types of e-mail attachment in order to reduce the risk of virus infection. However it is important that you are aware of the main ways that viruses can be transmitted - listed below - so that you can act to protect your own PC. In all cases you should be wary of such items from an unknown / uncertain source.
E-mail attachments. Email attachments are perhaps the most common way for viruses to propagate, and should always be viewed with suspicion. Such a virus is triggered when the attached file is opened or executed. In the past there have also been cases where loop-holes in mail programs have been exploited, and a virus has been triggered simply by reading an email. We are not aware of any such loopholes currently, but it is always possible that another may emerge and constitute a risk until the email program is fixed. The viruses and attachments faq page gives more details of the risks involved and explains best practice for dealing with attachments.
Network Shares. Many viruses now attempt to duplicate by copying themselves to shared network resources. Although such resources can take several forms, the most vulnerable are shared folders. When a virus identifies a shared folder it will attempt to copy itself into it, thus risking infection of the PC housing the folder. However it is possible to limit this risk - by setting the access permissions for the folder. If you have set-up any shared folders we ask that you read this page on shared folder security and take appropriate action to secure them. Please note that all shared folders on Computing Service servers are secured as standard.
Removable media — usb flash or pen drives, compact disks, floppy disks, portable hard drives. As these are often used in a variety of machines you risk transporting a virus from one machine to another.
Web downloads. Any material downloaded from the web (programs or documents) could contain a virus.
Documents. Many documents and spreadsheets can contain useful macros. However macro viruses also exist - these use the functionality of macros to spread themselves to further files and can make alterations to the files infected.
Given the many ways in which viruses can spread, it is essential that individual desktop computers have their own virus protection. To protect against viruses on your PC, you need to have an anti-virus package installed and kept up to date. The University supplied anti-virus package, Sophos, can provide this protection.
Hoax virus warnings
Many virus warnings circulated by e-mail are hoaxes, which can lead to a great deal of wasted time. If you receive a virus warning in an e-mail from an unofficial source, please do not automatically send it everyone you know. Alert the Computing Service by forwarding the message to the virus administration mailing list virusadmins@essex.ac.uk. This will ensure that the appropriate people are aware of the situation and they will deal with it accordingly.
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