These scripts can't do that much other than turn itself into a virus. When a macro turns into a virus, it can easily turn a small fraction of script into a dangerous virus that easily spreads. To spread easily, it repeats the script quickly in interminable multitudes. Whenever they turn into viruses, the scripts will become more lengthy and harmful. Scripts like these end up slowing down the user's computer. Stormworm is a good example of being an invisible virus or trojan. Many viruses are made out of Macros.
Never underestimate a Macro.