You should spend about 20 minutes on Questions 1-5, which are based on Reading Passage below.

COMPUTER VIRUSES

Computers can do anything: from running spread sheets, word processors and power stations to music synthesizers and missile control systems. And because computers can do anything, they can in particular run viruses and any other nasty software.

Viruses are unique in their abilities, as they can stop many computers at once. This would be much more serious for a small company than normal faults that affect only one PC at a time. Thus, viruses rank with hazards like power cuts and fire in their effect and speed of action. Worse than fire though, people may find that they cannot take their work elsewhere, for if they did, they might simply take the virus infection with them and bring more systems down. Secondly, viruses can distribute disinformation and bring shame to individuals or organisations: viruses may send malicious email apparently on behalf of the person whose computer has been infected.

A computer virus is a piece of program code that attaches copies of itself to other programs, incorporating itself into them, so that the modified programs, while still possibly performing their intended function, surreptitiously do other things. Programs so corrupted seek others to which to attach the virus, and so the infection circulates. Successful viruses lie low until they have thoroughly infiltrated the system, and only reveal their presence when they cause damage. The effect of a virus is rarely linked back to its originator, so viruses make attractive weapons for vandals. Computer viruses generally work by altering files that contain otherwise harmless programs. This is infection. When an infected program is invoked, it seeks other programs stored in files to which it has write permission, and infects them by modifying the files to include a copy of itself and inserting an instruction to branch to that code at the old program’s starting point. Then the virus starts up the original program, so that the user is unaware of its intervention. Viruses are classified as being one of two types: ‘research’ or ‘in the wild’. A research virus is one that has been written for research or study purposes and has received almost no distribution to the public. On the other hand, viruses that have been seen with any regularity are termed ‘in the wild’.

Before the spread of the Internet, most computer viruses were spread by removable media, predominantly floppy disks. Some viruses spread by infecting programs stored on these disks, while others installed themselves into the disk boot sector. Until floppy disks were replaced by other removable media, this was the most successful infection strategy and boot sector viruses were the most common in the wild for many years.

The term ‘computer virus’ is a popular catchall for all kinds of malicious software. A logic bomb is a destructive program activated by a certain combination of circumstances, or on a certain date, to delete information. A Trojan horse is any bug inserted into a computer program that takes advantage of the trusted status of its host by surreptitiously performing unintended functions. A worm is a distributed program that invades computers on a network.

It consists of several processes or segments that keep in touch through the network; when one is lost, the others conspire to replace it on another server. Viruses today have no distinct identity, but typically undergo mutation each time they copy themselves to other files. This, combined with various cryptographic techniques, makes modern viruses difficult to detect. False alarms have become an increasing problem, particularly with users sending chain email warning about supposed virus problems; ironically, the panics may cause more problems than the viruses they warn about. Email though has become the most popular way to disperse viruses today, because powerful commercial email packages are themselves programmable and users often configure email systems to helpfully run programs automatically.

Viruses are not difficult to develop. The majority of viruses are simple variants of others and many virus construction kits are readily available on the Internet. Viruses have been created since the 1960’s, although the term ‘computer virus’ was only formally defined by Fred Cohen in 1983. One of the first virus attacks occurred in late 1987 when, over a two-month period, a virus quietly insinuated itself into programs at a Middle East university. It was noticed because it caused programs to grow longer. Once discovered, it was analysed and an antidote devised. It was designed to slow processors down on certain Fridays, and to erase all files on Friday, 13 May.

It is common that certain viruses have been given names. Once discovered and named, programmers can create ‘antidotes’ that delete the viruses from the system. The obvious, but generally impractical defence against viruses is never to use anyone else’s software and never to connect with anyone else’s computer. A more practical approach to protect computers is to regularly or continuously run programs that recognise viruses and try to eliminate virus infections before they do too much damage. Because new viruses are being devised every day, it is important and sensible to keep detection programs up to date, by, for example, a regular subscription from a reputable firm, and to minimise risky procedures, such as sharing information as infrequently as possible.

All protection approaches are trade-offs. Eternal vigilance on the part of users is important, and, above all, education of users to the possible results of their actions