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Trojan Horse
A Trojan horse is malware that presents as desirable and helpful but actually causes harm to the system. A Trojan horse
generally attaches itself to a safe application. For example, it may be attached to a game downloaded over the Internet.
Figure 9.4 shows how a Trojan horse makes a backdoor into the system that hackers can use to get into the system.
Hackers can keep track of everything that happens on the system and take control of it by looking at or damaging its data.
Worms
A worm is a malicious program that replicates itself. So, a networked device could have several copies of a worm
infecting many files. Like viruses, to spread a worm for the first time, an email or an instant chat is sent with attachments
from seemingly trustworthy senders. Once the infected email attachment is opened, the worm is downloaded onto
the recipient's system. Then it replicates itself and spreads to the devices of the contacts (again via mail) in the user's
mail account. For example, the Code Red worm can make around 3 lakh copies in a few hours.
Spyware
The spyware secretly collects information from a system. One may unknowingly install spyware on their device when
downloading files or software from dubious websites or by opening suspicious email attachments. Therefore, one
must exercise caution while opening emails or downloading files from suspicious sources. Some common signs of a
system under the spyware attack are: getting constant error messages, random icons being displayed on the desktop,
or unwanted opening of tabs while browsing the Internet
Adware
An adware is a software that displays advertisements to users of the Internet and mobile applications. Advertisements
can show up in different ways in an app, such as a static box, a banner, a full screen, a video, or a pop-up (Figure 9.5).
These advertisements generate revenue for developers. Adware may also record user activities and pass them on to
the relevant businesses for money. Adware may also act as spyware by collecting private and sensitive information.
Figure 9.5: Adware
Societal Impacts 275

