Security Aspects

A computer is considered safe when it is not connected to a network or the Internet because it is then isolated from outside connections. Without a link to external devices or computers, it is not exposed to security threats coming from the network, so illegitimate access or misuse becomes much harder.

A computer virus is a piece of software code created to perform malicious activities and harm a computer system’s resources such as CPU time, memory, personal files, or sensitive information. It spreads by infecting other computer systems when it comes into contact with them, usually by inserting its code into executable files. Some viruses mentioned in the chapter are CryptoLocker, ILOVEYOU, MyDoom, Sasser, Netsky, Slammer, and Stuxnet.

A worm is different from a virus in two main ways:
- A worm does not need a host program to insert its code into; it is a standalone program.
- A virus usually needs human triggering to replicate, but a worm replicates on its own and can spread through the network.

So, a worm is self-contained and self-replicating, while a virus depends on a host file and user action.

Ransomware extracts money by blocking access to the user’s data or by threatening to publish personal data online. It then demands a ransom payment to restore access or avoid disclosure. Some ransomware also encrypts the data, making it very difficult to access unless the ransom is paid.

A Trojan got its name from the ancient Greek story of the Trojan horse. In that story, soldiers were hidden inside a wooden horse that looked harmless but was used to defeat the city of Troy. Similarly, a Trojan malware looks like legitimate software but hides malicious actions inside it.

Adware generates revenue for its creator by displaying online advertisements, such as pop-ups, web pages, or installation screens. Once it infects many systems, it earns money either by showing ads or through a pay-per-click mechanism, where the creator is paid based on the number of clicks on the ads.

A keylogger can create two major threats:
1. It can record passwords, emails, private conversations, and other sensitive information typed by the user and send them to an external entity.
2. It can expose login credentials, banking details, and personal data, leading to identity theft, account misuse, or financial loss.

So, keyloggers threaten both privacy and security.

A virtual keyboard is safer than an on-screen keyboard because the virtual keyboard randomises the key layout every time it is used. The on-screen keyboard usually has a fixed QWERTY layout, which can be exploited by keyloggers. Randomising the layout makes it very difficult for a keylogger to identify which key was pressed.

The chapter lists these modes of malware distribution:
- Downloaded from the Internet: Malware may be unknowingly downloaded by the user, especially disguised as free software or files.
- Spam Email: Malware may arrive as unsolicited emails with harmful links or attachments.
- Removable Storage Devices: Infected pen drives, SSD cards, music players, or phones can transfer malware to other systems.
- Network Propagation: Some malware, like worms, spread from one computer to another through a network connection.