In the growth of viruses hardly very quickly, This pest code can be classified in 3 kinds of faction: virus, worm and Trojan, Horses, and also some programs having bug.
Virus, Virus have ability of bad for reproducing is thyself and consist of gathering of code available for modifying code goals being run, or modify internal structure of code goals, so that code goals before run forced to implement viruses. Virus often present unwelcome message, destroy display, vanish memory C-mos, destroy hard disk inside information etc. generated by Effect is viruses experience enough growth serious recently. Virus example: Brain Ohe half, Die hard, XM/Laroux Win95/CIH
Worm, Worm is addressed to program copying their self to ONLY memory computer. Basic difference from worm and viruses is, is goals infection code or no. Virus goals infection code, but worm no. Worm only living in memory. Worm earn swiftly multiply x'self and usually done at media LAN or Internet, resources network which infection would [used up/finished] the bandwidth inundated by worm which will result the lag of data stream. Example of worm: I-Worm/Happy99(Ska), I-Worm/ExploreZIP, Sobig, Nimda, Code, Red, Sircam. Worm generally in form of file executable ( extension. EXE or. S.C.R), which enclosed ( attach) at enamel. But that way, there are some type worm which in form of script which written in language Visual Basic ( VBScript).