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Introduction to Computer Viruses & Security

What Is a Computer Virus?

A computer virus is a special kind of computer program which:

• Spreads across disks and networks by making copies of itself, usually surreptitiously.

• Can produce undesired side-effects in computers in which it is active.

How Infection Occurs

In order to infect a computer, a virus has to have the chance to execute its code.

Viruses usually ensure that this happens by behaving like a parasite, i.e. by modifying another item so that the virus code is executed when the legitimate item is run or opened. Good vehicles for viruses include the parts of a disk which contain code executed whenever that disk is booted, and documents which contain macros executed whenever that document is opened with the relevant application. As long as the virus is active on the computer, it can copy itself to other files or disks that are accessed.

How Viruses Escape Detection

The successful spread of a virus depends on how long it can replicate unnoticed, before its presence is made known by the activation of side-effects.

Viruses Use Two Main Methods of Disguise:

• Encrypting (scrambling) their code to avoid recognition.

• Preventing applications from seeing the virus in memory, by interrupt interception or (in the case of macro viruses) by disabling the options to view macros.

Virus Side-Effects

As well as self-replicating code, a virus normally contains a 'payload'. The former is like the propulsion unit of a missile; the latter is like the warhead it delivers. The payload can be programmed to have malicious side-effects. These effects can range from harmless messages to data corruption or destruction.

How Viruses Spread

Infections spread from machine to machine, and from organization to organization, in a number of ways.

Viruses Can Be Transmitted by:

• Booting a PC from an infected medium.

• Executing an infected program.

• Opening an infected file.

Common Routes for Virus Infiltration Include:

• Floppy disks or other media that users can exchange.

• E-mail attachments.

• Pirated software.

• Shareware.

Anti-Virus Measures

The fight against computer viruses involves five kinds of counter-measure:

• Preparation includes making backups of all software (including operating systems) and making a contingency plan.

• Prevention includes creating user awareness, implementing hygiene rules, using disk authorization software, or providing isolated 'quarantine' PCs.

• Detection involves the use of anti-virus software to detect, report and (sometimes) disinfect viruses.

• Containment involves identifying and isolating the infected items.

• Backup & Recovery The combination of manual and machine procedures that can restore lost data in the event of hardware or software failure. Routine backup of databases and logs of computer activity are part of a backup & recovery program.

• Checkpoint/Restart A method of recovering from a system failure. A checkpoint is a copy of the computer's memory that is periodically saved on disk along with the current register settings (last instruction executed, etc.). In the event of any failure, the last checkpoint serves as a recovery point. When the problem has been fixed, the restart program copies the last checkpoint into memory, resets all the hardware registers and starts the computer from that point. Any transactions in memory after the last checkpoint was taken until the failure occurred will be lost.

Computer Security

• Security The protection of data against unauthorized access. Programs and data can be secured by issuing identification numbers and passwords to authorized users of a computer. However, systems programmers, or other technically competent individuals, will ultimately have access to these codes.

• Passwords can be checked by the operating system to prevent users from logging onto the system in the first place, or they can be checked in software, such as DBMSs, where each user can be assigned an individual view (subschema) of the database. Any application program running in the computer can also be designed to check for passwords. Data transmitted over communications networks can be secured by encryption to prevent eavesdropping. Although precautions can be taken to detect an unauthorized user, it is extremely difficult to determine if a valid user is performing unauthorized tasks. Effective security measures are a balance of technology and personnel management.

NB Computer Security Act The first step in improving the security and privacy of information contained in federal computer systems. Signed January 8, 1988 by President Reagan, the Act: Establishes a central authority for developing guidelines for protecting unclassified, but sensitive information stored in government computers. Requires each agency to formulate a computer security plan, tailored to its own circumstances and based on the guidelines. Mandates that each agency provide training for its computer employees on the threats and vulnerabilities of its computer systems. Ensures that the National Security Agency and other defense-related government agencies not control computer security standards in civilian agencies of government.