Infectious malware is comprised of viruses and worms, while Trojans, backdoors and rootkits are concealed pieces of malicious code. Last, but not least, malware for profit gathers spyware, botnets, keystroke loggers, as well as telephony dialers.
Computer viruses are pieces of software that can replicate themselves and stealthily infect the host computer. Due to the fact that viruses are associated with destructive behaviors, they are wrongfully used to define multiple types of malware. Depending on its complexity, the initial virus may modify its next copies, in order to escape the simple string detection algorithms in antivirus software. Viruses can spread using either the network / Internet, or by infecting files on removable media (floppy disk, CD or USB drives).