▁number ▁allows ▁a ▁given ▁user ▁ID ▁to ▁be ▁associated ▁with ▁more ▁than ▁one ▁username , ▁each ▁having ▁its ▁own ▁shell . ▁ ▁Security ▁consider ations ▁The ▁presence ▁of ▁a ▁' to or ' ▁account ▁( or ▁the ▁presence ▁of ▁more ▁than ▁one ▁account ▁with ▁a ▁user ▁ID ▁of ▁ 0 ) ▁triggers ▁a ▁warning ▁in ▁many ▁security ▁aud iting ▁systems . ▁This ▁is ▁valuable , ▁since ▁if ▁the ▁system ▁administrator ▁did ▁not ▁intend ▁for ▁a ▁second ▁super user ▁account , ▁then ▁it ▁may ▁mean ▁that ▁the ▁system ▁has ▁been ▁comprom ised . ▁ ▁It ▁may ▁be ▁argued ▁that ▁even ▁an ▁intent ional ▁' to or ' ▁account ▁is ▁a ▁security ▁risk , ▁since ▁it ▁provides ▁a ▁second ▁point ▁of ▁attack ▁for ▁someone ▁trying ▁to ▁ill ic it ly ▁gain ▁super user ▁privileges ▁on ▁the ▁system . ▁However , ▁if ▁passwords ▁are ▁chosen ▁and ▁guard ed ▁carefully , ▁the ▁risk ▁increase ▁is ▁minimal . ▁ ▁For ▁example , ▁Net B SD ▁ships ▁with ▁a ▁disabled ▁' to or ' ▁account , ▁meaning ▁that ▁there ▁is ▁no ▁password ▁with ▁which ▁one ▁can ▁log ▁into ▁the ▁system ▁as ▁' to or '. ▁This ▁is ▁not ▁a ▁security ▁risk ▁in ▁itself , ▁though ▁it ▁may ▁generate ▁security ▁warnings ▁as ▁previously ▁described . ▁However , ▁if ▁the ▁system ▁is ▁comprom ised , ▁an ▁administrator ▁may ▁be ▁less ▁likely ▁to ▁notice ▁the ▁en abling ▁of ▁a ▁disabled ▁account ▁than ▁the ▁creation ▁of ▁a ▁new ▁one , ▁especially ▁if ▁he ▁has ▁become ▁acc ustom ed ▁to ▁ign oring ▁warnings ▁about