Q. 47 What are dialogue boxes ?
Q. 49 Explain in brief the following programs of MS-Windows :
Q. 50 Define “security” with respect to an operating system. Explain the different elements of security?
Q. 51 Discuss in brief threats to security in any computing environment.
Q. 52 What are attacks on security ? Explain in short the ways in which a system can be attacked.
Q. 53 What are computer worms ? Explain its mode of operation.
Q.54 What is a computer virus ? State various types of viruses and the basis on which they are classified.
Q. 55 What are the different methods by which virus can infect other programs ?
Q. 56 How generally a virus operates ?
Q. 57 Discuss virus detection, removal and prevention philosophies.
Q. 58 Differentiate between computer worms and computer viruses.
Q. 59 What is the difference between a Worm and a Virus? Explain how these can be prevented.
Q. 47 What are dialogue boxes ?
Ans: i) Dialogue box is a window, used by the application to interact with the user.
ii) A dialogue box can also be used to display information or to get user input and also for a combination of these two functions.
iii) Dialogue boxes are of two types : (i) Model dialogue box ii)Modeless dialogue box.
iv) A dialogue box where an application can continue only after the user has responded to the dialogue is called model dialogue box.
v) A dialogue box, which allows user to continue without responding to it is called modeless dialogue box.
Question Number 48 is Skiped
Q. 49 Explain in brief the following programs of MS-Windows :
(i) Program Manager
(ii) File Manager
(iii) Control Panel
Ans : MS-Windows environment provides following programs which play very important roles.
1) Program Manager :
(a) The Program Manager starts executing along with MS-Windows.
(b) This provides user interface to start and stop applications.
(c) Itis used to organize various applications into different groups.
(d) It also indicates how each group contents are controlled and displayed on the screen.
(e) It is also used to end the MS-Windows session.
2) File Manager :
(a) This helps organize user files and directories.
(b) This is used to traverse through the file system and change drives, to search, copy, move, create or delete files and directories.
(c) Applications can be started directly from the File Manager.
3) Control Panel :
(a) It can be used to choose or change the color schemes in the applications, select and display the background of the screen, select border width and other border characteristics, cursor size and shape etc.
(b) Fonts also managed by controlpanel.
(c) It is also used to configure printers and other ports on the PC.
Access and Security Aspects of O.S.
Q. 50 Define “security” with respect to an operating system. Explain the different elements of security?
Ans : 1) Security is concerned with the ability of the operating system to enforce control over the storage and transportation of data in and between the objects, that the operating system supports.
2) In multiuser operating systems, the concepts of security and protection are very important.
User programs should not interfere with one another or with the operating system.
3) In general, Secure Systems are those, which control, through the use of specific security features, access to information that only properly authorized individuals or processes operating on their behalf will have access to read, write, create or delete.
4) There are three main elements of security viz. Confidentiality, integrity and availability.
(i) Confidentiality :
Confidentiality ensures that information is not accessed in an unauthorized manner. It is
generally related to the Read operations.
(ii) Integrity :
Integrity ensures that the information is not amended or deleted by an unauthorised manner.
It is generally related to Write operations.
(iii) Availability :
It ensures that information is available to the authorised users at right time.
Q. 51 Discuss in brief threats to security in any computing environment.
Ans : 1) Sharing and protection are requirements of modern computing environments. But these two are contradictory to each other as more sharing gives rise to possibility of more security threats.
2) The major threats to security in any computing environment can be categorized as follows :
(i) Tapping : Unauthorised use of servicing.
(ii) Disclosure : Unauthorised disclosure to information.
(iii) Amendment : Unauthorised alteration or deletion of information.
(iv) Fabrication : Unauthorised fabrication of information.
(v) Denial : Denial of service to the authorized users.
3) The security threats are shown in the following figure.
4) Out of these five security threats, the first fwo, viz. tapping and disclosure, are categorized
as passive threats and the other three as active threats.
5) It is clear that in both the cases (i) and (ii), information goes to the third party. But, the
difference is that in tapping the third party accessed information without knowledge of other two parties. Whereas in disclosure the source party willingly discloses information to the third party.
Q. 52 What are attacks on security ? Explain in short the ways in which a system can be attacked.
Ans : The security system can be attacked and penetrated in a number of ways as follows :
1. Authentication :
Authentication means verification of access to the system resources. Following are some of the ways in which authentication may take place :
(i) By stealing and using somebody else’s password and then use it.
(ii) Use of vendor supplied password which can be used by only system administrator.
(iii) Finding password by trial and error (i.e. guess) method.
(iv) If a user logs on and then goes off, an intruder can use that terminal.
(v) Writing dummy login programs to fool the user.
2. Browsing :
(i) In some systems, there exist files with access controls, which are very permissive.
(ii) One can browse through the system file to get this information, after which, unprotected files/databases could be easily accessed.
(iii) Confidential information could be read or even modified.
3. Trap doors:
(i) Sometimes, software engineers leave some secret entry point to modify their programs.
These are called trap doors.
(ii) They can be misused by others.
4. Electric data capture :
Use of active or passive wire traps, or mechanism to pick up the screen radiation and to recognize what is displayed on screen is called electric data capture.
5. Invalid parameters :
Passing invalid parameters may cause serious security violations.
6. Line trapping :
A special terminal is used to tap into a communication line. It causes access to confidential data.
7. Waste recovery :
By using some technique, deleted files can be recovered, password may be recollected.
8. Rouge software :
Certain programs like worms, viruses attack on system.
Q. 53 What are computer worms ? Explain its mode of operation.
Ans :
1. A computer worm is a complete program by itself. It is written in such a way that it spreads to other computers over a network.
2. But, while doing this, it consumes the network resources to a very large extent.
3. A computer worm can potentially bring the entire network to a grinding halt.
Mode of Operation:
4. Usually a computer worm does not harm other programs or data.
5. It just spreads, thereby consuming large resources such as transmission capacity or disk storage. It denies services to legitimate users.
6. A computer worm usually operates on a network. Each node on network maintains , a “mailing list”, which contains the names and addresses of the reachable machines on the network. The worm gets access to this list and using this, sends a copy of itself to all those addresses.
7. If the worm is intelligent, after reaching a node it checks whether a copy of itself already exist there or not. If exists, it does not create one more Copy.
8. If the worm in dumb, it just copies itself to all nodes. So, if one node’s address is at several places in network, then it would have several copies of the worm.
9. Safe guards against worms :
A worm can be prevented by strong security and various check points on the communication system.
Q.54 What is a computer virus ? State various types of viruses and the basis on which they are classified.
Ans :
1. A computer virus is a part of program, which is written with clear intention of infecting
other programs.
2. A computer virus is not a complete program by itself. It can not act independantly.
3. A computer virus causes direct harm to the system. It can corrupt code as well as data.
4. The classification of virus is based on what do it affects or where the virus resides.
5. There are five types of viruses given below :
(i) Boot sector virus
(ii) Memory resident virus
(iii) File specific virus
(iv) Command processor virus
(v) General purpose virus.
Q. 55 What are the different methods by which virus can infect other programs ?
Ans : There are five well known methods by which a virus can infect other programs :-
(i) Append: In this method the viral code appends itself to the unaffected programs.
(ii) Replace: In this case, the viral code replaces the original executable program completely or partially to carry out some funny actions.
(iii) Insert : In this case, the viral code is inserted in the body of an executable code to carry out some funny or undesirable actions.
(iv) Delete : In this case, the viral code deletes some code from the executable program.
(v) Redirect : This 15 an advanced approach employed by the authors of sophisticated viruses. The normal control flow of a program is changed to execute some other code, which could exist as an appended portion of normal program.
Q. 56 How generally a virus operates ?
Ans:
1. A virus works in a number of ways. Normally, the developer of a virus has to be a very bright person who knows the operating system very well in order to break it.
2. This person produces interesting or useful program such as a good game or utility. However,
this program has some viral code embendded in it.
3. Typically, it is developed under MS-DOS, as viruses are very popular on the PCs.
4. This program is then published on the public bulletin board system or it is distributed to
people free of charge.
5. Tempted by its contents and the price, the user acquires it and then starts using it after
copying it onto the machine.
6. At this stage, the virus can be said to be in a nascent state. After executing the game or the
utility i.e. the host program, the virus also executes, which allows it to spread to other programs on the machine and infect them.
Q. 57 Discuss virus detection, removal and prevention philosophies.
Ans :
(i) Virus detection :
- Normally, a virus detection program checks the integrity of the binary files.
- The program maintains a check sum on each file. A mismatch in it indicates virus.
- Some programs reside in the memory and continuously monitor certain memory and I/O operations for guarding against any suspicious behavior.
(ii) Virus removal :
- A generalized virus removal program is very difficult to imagine due to the multiplicity of the viruses and the creativity with which they are constructed.
- However, for some viruses, bit pattern in code can be predicted.
- In this case virus removal program scans the disk for the patterns of known viruses.
On detection, it removes them. But, if the virus has already damaged data, then recovery of data is almost impossible.
(iii) Virus prevention :
- User cannot cure the data (recover) after viral affection. Hence the best way is to prevent viruses.
- For this user must buy official, legal copies of software from reliable stores or sources.
- One should be extremely careful about picking up free, unreliable or illegal software.
- Frequent back-ups and running of monitoring programs also help in detection, and thus subsequent prevention of different viruses.
Q. 58 Differentiate between computer worms and computer viruses.
Ans :
Computer worms :
i) A computer worm is a complete program.
ii) A computer worm can act independently.
iii) Generally it do not cause direct harm to computer system.
iv) It just goes on spreading on to network and consumes network resources to a large extent.
Computer viruses :
i) A computer virus is not a complete program, but a part of program.
ii) A computer virus can not act independently.
iii) It causes direct harm to the computer system. It has been written with clear intention of infecting others.
iv) A computer virus corrupts codes and data.
Q. 59 What is the difference between a Worm and a Virus? Explain how these can be prevented.
Ans :
Difference between a Worm and a Virus : Refer Q. No. 58.
1) Worm Prevention : A worm can be prevented by strong and various check points on communication system.
2) Virus Prevention :
(a) Users cannot cure the data after viral affection. Hence the best way is to prevent
viruses.
(b) For this user must buy official, legal copies of software from reliable stores or sources,
(c) One should be extremely careful about picking up free unreliable or illegal software.
(d) Frequent back-ups and running of monitoring programs also help in detection, and
thus subsequent prevention of different viruses.
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