What do Viruses, Trojans, and Other Malware Actually Do?

all what have you mentioned above do the following:

harm you Pc

Malfunction to the PC tasks and fuctions

slow the PC performance , connection and hang it up

corruption of files, folders and software.

disable start up programs

disable the task manager

make your PC running in inappropriate manner

spying on your PC

stealing your Important and sensitive data

web browser  malfunction

etc>>

• Malware causes your connection to slow down
• Malware causes your computer to slow down; badly written code can cause your computer to crash.
• Malware can cause your computer to display error messages continually.
• Malware could cause your computer to be incapable of shutting down or restarting as it keeps certain processes active.
• Malware could be used for identity theft to gather personal information or data from your computer.
• Malware can hijack your browser to redirect you to sites for its purposes.
• Malware can infect your computer and use it as a server to broadcast various files or attacks.
• Malware can send spam through and to your inbox.
• Malware could send emails you did not write getting you or your company in trouble.
• Malware can infect your computer giving an attacker control of your system and your resources, like your connection.
• Malware can cause new and unexpected toolbars to appear.
• Malware can cause new and unexpected icons to appear on your desktop.
• Malware can be invisible and have no known or noticeable affect and run on your computer undetected if it’s well written.

First of all, computer virus and trojans together with worms and bots are all identified as classes of Malicious Software or the so-called MALWARE. Malware is a code or software that is developed to damage, steal and corrupt files or systems. 

Viruses or computer virus works by inserting a copy of itself and becoming part of a program. It easily spreads from one computer to another through network, USBs and the like. Mostly, theses viruses are in executable file which is the black .exe square appearing on flash drives. However, these viruses won’t be able to speed if the use do not run the host file or program, that means once the host is executed, viruses automatically and enthusiastically spread. It copies itself and spreads all over the system.

A Trojan is another type of malware which was named after the wooden horse the greeks used to infiltrate Troy. It is a very harmful software that looks legitimate. Typically, users are tricked to loading and running/installing file in their systems. Once it is activated, it attacks the host and most things one can see are popping up windows or chasing desktops. IT also damages the host by deleting and stealing datas and/or activating or spreading viruses. One thing you must know that Trojans do not reproduce, it only spreads though user interaction such as opening email attachment and executing a malicious file from the internet.

Basm allah alrahman alrahim

Loraine Domingo answer can be a reference

What can I say more ?

virus like real human virus live on cell and spreed through it (spreed through another program at PC)

worms like virus make harm but it dose not use another cell I mean program

trajons hourse like the famus story , it disappear and attack , trajons make alot of things like open backdoors at your computer for the thieves (hackers and crackers) to steal your passwords , cridts and informations

there are alot of other things like adware , bots (bad robots) , spyware (can be used by some goerments)

i fully agree with the answers been added by experts....thanks.

they corrupt your saved files and might delete your important work