Computer viruses and network security is important. There are things that are not public information. Therefore it is good to be a weare of possible network security problems.
The next thing usually the person whose computer might be infected with virus, panics. The person might think that all the work that have been done is missing. That could be true, but in most cases viruses have not done any harm jet, but when one start doing something and are not sure what you do, that might be harmful. When some people try to get rid of viruses they delete files or they might even format the whole hard disk like my cousin did. That is not the best way to act when the person think that he has a virus infection.
What people do when they get sick? They go to see a doctor if they do not know what is wrong with them. It is the same way with viruses, if the person does not know what to do they call someone who knows more about viruses and they get professional help.
If the person read email at their PC or if they use diskettes to transfer files between the computer at work and the computer at home, or if they just transfer files between the two computers they have a good possibility to get a virus. They might get viruses also when they download files from any internet site. There was a time when people were able to be sure that some sites we secure, that those secure sites did not have any virus problems, but nowadays the people can not be sure of anything. There has been viruses even in Microsoft's download sites.
In this report I am going to introduce different malware types and how they spread out and how to deal with them. Most common viruses nowadays are macro viruses and I am going to spend a little more time with them. I am going to give an example of trojan horses stealing passwords.
There are a couple of different types of computer viruses: boot sector viruses, parasitic viruses, multi-partite viruses, companion viruses, link viruses and macro viruses. These classifications take into account the different ways in which the virus can infect different parts of a system. The manner in which each of these types operates has one thing in common: any virus has to be executed in order to operate. 
Most viruses are pretty harmless. The user might not even notice the
virus for years. Sometimes viruses might cause random damage to data files
and over a long period they might destroy files and disks. Even benign
viruses cause damage by occupying disk space and main memory, by using
up CPU processing time. There is also the time and expense wasted in detecting
and removing viruses.
According to an administrator of AOL, the Trojan steals passwords and
sends an E-mail to the hackers fake name and then the hacker has your account
in his hands.
A CAP macro virus, now widespread, infects macros attached to Word 6.0 for Windows, Word 6.0.1 for Macintosh, Word 6.0 for Windows NT, and Word for Windows 95 documents.
What makes such a virus possible is that the macros are created by WordBASIC and even allows DOS commands to be run. WordBASIC in a program language which links features used in Word to macros.
A virus, named "Concept," has no destructive payload; it merely spreads, after a document containing the virus is opened. Concept copies itself to other documents when they are saved, without affecting the contents of documents. Since then, however, other macro viruses have been discovered, and some of them contain destructive routines.
Microsoft suggests opening files without macros to prevent macro viruses from spreading, unless the user can verify that the macros contained in the document will not cause damage. This does NOT work for all macro viruses.
Why are macro viruses so successful? Today people share so much data,
email documents and use the Internet to get programs and documents. Macros
are also very easy to write. The problem is also that Word for Windows
corrupts macros inadvertently creating new macro viruses.
Corruption's also creates "remnant" macros which are not infectious,
but look like viruses and cause false alarms. Known macro virus can get
together and create wholly new viruses.
Almost all virus detected in the Helsinki University of Technology have been macro viruses, according to Tapio Keihänen, the virus specialist in HUT.
Before macro viruses it was more easy to detect and repair virus infections with anti-virus programs. But now when there are new macro viruses, it is harder to detect macro viruses and people are more in contact with their anti-virus vendor to detect an repair unknown macro viruses, because new macro viruses spread faster than new anti-virus program updates come up.
Most of the writers are young men. There are also few university students, professors, computer store managers, writers and even a doctor has written a virus. One thing is common to these writers, all of them are men, women do not waste their time writing viruses. Women are either smarter or they are just so good that never get caught. 
A computer is infected with a boot sector virus if it is booted from
an infected floppy disk. Boot sector infections cannot normally spread
across a network. These viruses spread normally via floppy disks which
may come from virtually any source:
A file virus infects other files, when the program to which it is attached is run, and so a file virus can spread across a network and often very quickly. They may be spread from the same sources as boot sector viruses, but also from sources such as Internet FTP sites and newsgroups. Trojan horses spread just like file viruses.
A multipartite virus infects boot sectors and files. Often, an infected
file is used to infect the boot sector: thus, this is one case where a
boot sector infection could spread across a network.
As an example, in one unnamed company: over a long period of time, the files in a server were corrupted just a bit. So backup copies were taken from the corrupted files. And after they noticed that something was wrong, it was too late to get back the data from the backups. That kind of event is the worst that can happen for the uses.
There is also talk that viruses have done something to hardware like
hard disk or monitor. Viruses can not do any harm to hardware but they
can do harm to programs and for example to BIOS so that computer does not
start after that. Usually you can start the computer from a boot diskette
if the computer does not start otherwise.
How many Mac viruses there are? I found out that there are about 2-300
Mac-specific viruses. There are virtually no macro viruses which have a
Mac-specific payload, but all macro viruses can infect on Macs and other
platforms which runs Word 6.x of better.
In general, there are virtually no non-experimental UNIX viruses. There have been a few Worm incidents, most notably the Morris Worm,. the Internet Worm, of 1988.
There are products which scan some Unix systems for PC viruses. Any machine used as a file server (Novell, Unix etc.) can be scanned for PC viruses by a DOS scanner if it can be mounted as a logical drive on a PC running appropriate network client software such as PC-NFS.
Intel-based PCs running Unix e.g. Linux, etc. can also be infected by a DOS boot-sector virus if booted from an infected disk. The same goes for other PC-hosted operating systems such as NetWare.
While viruses are not a major risk on Unix platforms, integrity checkers
and audit packages are frequently used by system administrators to detect
file changes made by other kinds of attack.
A computer virus can cause unusual screen displays, or messages - but most don't do that. A virus may slow the operation of the computer - but many times that doesn't happen. Even longer disk activity, or strange hardware behavior can be caused by legitimate software, harmless "prank" programs, or by hardware faults. A virus may cause a drive to be accessed unexpectedly and the drive light to go on but legitimate programs can do that also.
One usually reliable indicator of a virus infection is a change in the length of executable (*.com/*.exe) files, a change in their content, or a change in their file date/time in the Directory listing. But some viruses don't infect files, and some of those which do can avoid showing changes they've made to files, especially if they're active in RAM.
Another common indication of a virus infection is a change to the reassignment of system resources. Unaccounted use of memory or a reduction in the amount normally shown for the system may be significant.
In short, observing "something funny" and blaming it on a computer virus is less productive than scanning regularly for potential viruses, and not scanning, because "everything is running OK" is equally inadvisable.
Second,make sure that you should get sure that it is virus and what virus it is. It is important to know what kind of virus we are dealing with. Companies that make anti-virus programs knows what different viruses does and you can ether call them and ask about that viruses or you can go to their web pages and read about the virus you have.
When you start you computer you should do it from a clean (non-infected) floppy diskette and after that run the virus program. The boot diskette should be write protected so that virus can not infect the boot diskette too.
It is good to take a backup of the file that was infected. Virus program could do some damage to the file and that is why it is good to have a backup.
It is good to let you administrator to know about the virus, so viruses would not spread around so much. In TKK PC classes are protected by anti-virus program and that virus program reports to a person, responsible for virus protection.
As an example in one unnamed Finnish company all information was mailed in email attachments. There was this one Word document that was mailed to everybody. That email attachment was infected by a macro virus. Everyone got the infected attachment and those who opened that attachment by Word got that CAP-macro virus. After all there were a few thousand infections. It took lots of time and money to clear that virus.
One can protect the computer against boot sector viruses by setting the BIOS to start from a hard disk rather than from a floppy disk.
Write protection is a good way to prohibit against viruses. Write protection
works well in floppy disks, Windows NT and UNIX, but not that well in Windows
There are over ten good anti-viral programs. Most knows programs are Data Fellows F-Prot, EliaShim ViruSafe, ESaSS ThunderBYTE, IBM AntiVirus, McAfee Scan, Microsoft Anti-Virus, Symantec Norton AntiVirus and S&S Dr Solomon's AVTK.
On a day-to-day basis, the average corporation should be very interested
in the scan time; these impact strongly the users, who should be scanning
hard drives and disks on a daily basis. If a product takes too long to
carry out these basic tasks, users will be unwilling to wait, and will
stop using it. This is clearly undesirable - the perfect anti-virus product
would be one which takes no time to run and finds all viruses.
The knowledge of viruses was quite poor in all sectors: government, local authorities and companies. Respondents' knowledge of viruses was best in government organizations. How importance is virus prevention? The most positive attitude to virus prevention was in government organizations.
90% of the government organizations used some kind of anti-virus program, the same in local authority organizations was about 55 % and in companies it was over 60 %. 
It is not punished to make or spread viruses in Finland, according today's penal code. If viruses make harm to somebody that could be punished. Nobody has been punished for that in Finland, even though some Finns has made viruses, for example Finnish Spryer. That virus formatted about 600 hard disks and did lots of damage. They say that it was made in Espoo, but they never got the persons that made that virus.
Virus business in Finland is pretty big. Businesses that have specialized in viruses have about 100 million in sales together. It costs money to stop working and clean up the viruses. Computer viruses put in danger general safety, says Pihlajamäki from Ministry of Justice. It is dangerous if viruses gets to programs that control trains or airplanes.
Computer viruses can also be used as a weapon. It is sad that America
used computer viruses to slay and to make Iraq's computers non-functional.
Dave Kenney answered from National Computer Security Assoc: "There is one macro virus for MSWord that is received as an attachment to MS Mail messages. If a user has Word open, and double clicks to see the contents of the attachment, MS Word and the open document is infected. Then the document is mailed to three other users listed in the original user's address book."
"The only information that is leaked is the thing you should be worried about, your password! The trojan sends an E-mail to the hackers fake name and then he has your account at his hands," wrote CJ from American Online.
"Rarely, a Word macro virus may accidentally pick up some user information and carry it along; we know of one case where a macro virus "snatched" an innocent user macro that contained a password, and spread it far outside the company where that happened. In the future, however, it is entirely possible that more network-aware viruses will cause significant network security problems," wrote David Chess from IBM.
Marko Helenius wrote from Virus Research Unit, that there has been some cases when hackers have used trojan horses to gain information. There is one example in one finnish corporation where some money were transferred illegally a year ago. There has been a trojan in the University of Tampere too where the trojan pretend to be a host transfer program. The trojan saved users login name and password to hard disk.
There might be a virus in your computer if it starts acting differently. There is no reason to panic if the computer virus is found.
It is good to be a little suspicious of malware when you surf in the Internet and download files. Some files that look interesting might hide a malware.
A computer virus is a program that reproduces itself and its mission is to spread out. Most viruses are harmless and some viruses might cause random damage to data files.
A trojan horse is not a virus because it doesn't reproduce. The trojan horses are usually masked so that they look interesting. There are trojan horses that steal passwords and formats hard disks.
Marco viruses spread from applications which use macros. Macro viruses spreads fast because people share so much data, email documents and use the Internet to get documents. Macros are also very easy to write.
Some people want to experiment how to write viruses and test their programming talent. At the same time they do not understand about the consequences for other people or they simply do not care.
Viruses mission is to hop from program to other and this can happen via floppy disks, Internet FTP sites, newsgroups and via email attachments. Viruses are mostly written for PC-computers and DOS environments.
Viruses are not any more something that just programmers and computer
specialist have to deal with. Today everyday users have to deal with viruses.