Bootsector Virus:
A virus which attaches itself to the first part of the hard disk that is read by the computer upon bootup. These are normally spread by floppy disks.Note: Floppy disks are kind of outdated, so, perhaps, it's spread through portable hard disks or boot CDs.
Macro Virus:
Macro viruses are viruses that use another application's macro programming language to distribute themselves. They infect documents such as MS Word or MS Excel and are typically spread to other similar documents.This is a nightmare to every office workers. Once your computer is infected, your whole documents will be destroyed. So, always do backups!
Memory Resident Viruses:
Memory Resident Viruses reside in a computers volitale memory (RAM). They are initiated from a virus which runs on the computer and they stay in memory after it's initiating program closes.
Rootkit Virus:
A rootkit virus is an undetectable virus which attempts to allow someone to gain control of a computer system. The term rootkit comes from the linux administrator root user. These viruses are usually installed by trojans and are normally disguised as operating system files.
Polymorphic Viruses:
Well, poly means many and morph means form. So, this type of virus will replicate itself into many forms of file. Now, you might see it as a .pdf file. Next time you log in, it might have changed itself into a .dll file. It is extremely difficult to detect manually. Even some antivirus might miss it while scanning for viruses.
Logic Bombs/Time Bombs:
These are viruses which are programmed to initiate at a specific date or when a specific event occurs. Some examples are a virus which deletes your photos on Halloween, or a virus which deletes a database table if a certain employee gets fired.
This is my favorite type of virus, it is completely unpredictable, only the coder of the virus knows what will happen and when it will happen.
DeepFreeze might be able to counter this type of virus.
Important Note:
Knowing that viruses have a very big effect on your computer, you might want to update your firewalls and antivirus for protection. Everyday, hundreds(maybe thousands) of new viruses are made, with even more creative ways of infecting and surviving.
So, always keep your antivirus and firewalls up-to-date. However, do not get trapped by those fake antivirus providers. Only use trusted antivirus brands, such as Avira, Norton, AVG(Grisoft), and NOD32.
Thanks for reading.
Cyber Frost
