Class 7 Computer Book PDF

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Class 7 Computer Book With Solutions PDF Free Download

Computer Security

What do they mean by a threat? A threat, in the context of computer security, refers to anything that has the potential to cause serious harm to a computer system. A threat is something that may or may not happen, but has the potential to cause serious damage.

Threats can lead to attacks on computer systems, networks, and more.

A threat can be either “intentional” (i.e., intelligent; e.g., an individual cracker or criminal organization) or “accidental” (e.g., the possibility of a computer malfunctioning. or the possibility of a natural disaster such as an earthquake, a fire, or a tornado) or otherwise a circumstance, capability, action, or event.


Computer Viruses are nothing but a computer programs that do unwanted things with your computer resources eg. you are working on a PC and you are repeatedly receiving annoying messages Viruses: A virus is a small piece of software that piggybacks on real programs.

For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs) or wreak havoc.

E-mail viruses: An e-mail virus travels as an attachment to e-mail messages, and usually replicates itself by automatically mailing itself to dozens of people in the victim’s e-mail address book.

Some email viruses don’t even require a double-click-they launch when you view the infected message in the preview pane of your e-mail software.

Trojan horses: A Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk).

Trojan horses have no way to replicate automatically.

• Worms: A worm is a small piece of software that uses computer networks and security holes to replicate itself.

copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there,
as well.

• Virus Origins (

Why they are called Virus?

Computer viruses are called viruses because they share some of the traits of biological viruses.

A computer virus passes from computer to computer like a biological virus passes from person to

Similar to the way a biological virus must hitch a ride on a cell, a computer virus must piggyback on top of some other program or document in order to launch. Once a computer virus is running, it can infect other programs or documents.

What /who makes a virus?

who: People write computer viruses. A person has to write the code, test it to make sure it spreads properly, and then release it. A person also designs the virus’s attack phase, whether it’s a silly message or the destruction of a hard disk.


  1. The first is the same psychology that drives vandals and arsonists. For some people, that seems.

Virus History

Traditional computer viruses were first widely seen in the late 1980s, Some Virus the Melissa virus in March 1999 was spectacular in its attack. Melissa spread in Microsoft

Word documents sent via e-mail. The ILOVEYOU virus, which appeared on May 4, 2000, was even simpler. It contained a piece of code as an attachment. People who double-clicked on the attachment launched the code. It then sent copies of itself to everyone in the victim’s address book and started compiling files on the victim’s machine

Worms: A worm is similar to a virus by design and is considered to be a sub-class of a virus Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any human action.

A worm takes advantage of file or information transport features on your system, which is what allows it to travel unaided.

Worms use up computer processing time and network bandwidth when they replicate and often carry payloads that do considerable damage.

An example of worms: A worm called Code Red made huge headlines in 2001.

The Slammer worm (which caused mayhem in January 2003) exploited a hole in Microsoft’s SQL server. A worm called Storm, which showed up in 2007, immediately started making a name for itself. Storm used social engineering techniques to trick users into loading the worm on their computers.

Trojan Horse: A Trojan Horse is full of as much trickery as the mythological Trojan Horse it was named after The Trojan Horse, at first glance will appear to be useful software but will actually do damage once installed or run on your computer.

Language English
No. of Pages69
PDF Size20 MB

Computer Textbook With Solutions For Class 7 PDF Free Download

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