Who still remembers system viruses that were transmitted via floppy disks? Obviously today’s malicious codes no longer require a physical media to propagate – sometimes all it takes is an Internet connection to become infected. Since the first virus was created in a laboratory in the 1960s, viruses have greatly evolved. They now act independently, sending themselves by email to new victims or exploiting software flaws. They operate in increasingly diverse ways and it is sometimes difficult to determine to which family they belong because they may boast several propagation methods. Here are a few explanations of the different types of virus currently in circulation so that you have a better idea of how to protect yourself.
Among the most widespread of recent viruses are worms, which can act independently to spread over the Internet. Often possessing their own SMTP engine they can send themselves to everyone in their victim's address book, or spread via email, instant messaging or file-sharing networks. Some even circulate freely on the Internet searching for new victims to infect by exploiting software flaws.
Although they function differently from traditional viruses, Trojan horses are still considered as a member of the virus family even if they do often need another programme to hide within. They usually open up holes in security systems so that other malicious codes can install themselves or a hacker can take remote control.
Logic bombs are viruses which become active on a particular date or through the remote intervention of a hacker. There are also resident viruses, which remain in a computer's live memory and infect all the executable files launched. Non-resident viruses content themselves with infecting programmes running at the time of their execution.
Although they have almost disappeared from circulation,
system viruses caused devastation in the days of floppy disks by infecting computers' partition sectors and boot sectors.
Program viruses target one or more specific programs.
Macro viruses attack the macro functions of commonly-used office applications such as Word or Excel.
Script viruses use the features of the VBScript and JavaScript programs to infiltrate their victims' computers. As for
mass mailers, these are viruses which automatically email themselves to the addresses they find in their victim's computer.
Antivirus publishers have to name the variants of a malicious code from A to Z because of
mutant viruses. These are versions of viruses modified by hackers so that their behaviour or signature cannot be recognised. By so doing they hope to attack new victims in the time it takes the antivirus publishers to include the signature of the new variants in their databases. Some virus authors have pushed this logic even further by creating
polymorphic viruses which continually encrypt and decrypt their signature - by changing their form they become harder to detect. And, last but not least,
retroviruses which alter antiviruses' databases to make them unusable.
