Nowadays when people here the word virus they think keylogger or RAT(remote administration tool) but viruses/malware go alot more in depth then most people think
The main types i will be going over are
* Worms
* Trojan Horses(RAT)
* Logic Bombs
* Adware & Spyware
Worms
A worm is a program that can spread full copies or smaller versions of its self all over the harddrive and even over network sharing to other computer and even use your own email to send its self to everyone in your contacts. And it will either replace all your files with itsself or just keep spreading untill your harddrive has no more space left on it. One famous worm was the "IloveYou"
http://en.wikipedia.org/wiki/ILOVEYOU
How Do I Know If Im Infected?
With worms its pretty self evident, because you will notice either tons of junk files showing up or your hardrive space getting lower and lower, and the type of worm will depend on how fast it eats through your HD.
Trojan Horses
Trojan horses go by many names, RATS, remote admin tool, and the list is almost endless. The reason trojan horses are called remote administration tools are because thats just it, it allows them to access and control the infected computer from there own. RATS usually when ran create another copy of themself somewhere on the victims computer so that the slave can delete the original file and be nun the wiser. One way to check for trojans are check your "Start Up" (msconfig) or preform a portscan on your localhost.
How Do I Know If Im Infected?
Some signs signs that your infected with a trojan is that your anti virus/firewall could be disabled, or random events such as your wallpaper changing, random mouse movements, files being deleted without knowledge.
Logic Bombs
You dont really hear much about logic bombs anymore because there not that widely used.But just a little something about them.Logic bombs are highly destructive and can range from changing bytes of data on the HD to making the entire HD unreadable.Logic bombs are most commonly installed by insiders with access to the system.Like in 2008 an insider attempted to load a logic bomb with a timer onto a computer system at the Federal National Mortgage Association but was unsuccessful and was arrested.
How Do I Know If Im Infected?
At first you can have no knowledge because most logicbombs have timers to execute hours, days, weeks, months after file execution. But after it executes like a worm it will be self evident but unlike the worm filling space, you will notice a loss of data on the HD.
Adware & Spyware
Have you ever downloaded a program you thought was safe but all it did was give you popups? Thats typical adware. Adware is advertising software they arnt high security risks most of the time like the above. And most of the spyware is included with adware, spyware is more dangerous than adware because it "mines" data such as browsing history, emails, and sometimes creditcard #s and either uses it for marketing or sells it to other companies.
How Do I Know If Im Infected?
Adware is pretty obvious because you will get popups and stuff like that, but spyware is alot harder to notice sometimes.
Keep Rocking, Keep Hacking