+ a + field & second = was + it + clear + % 2 8 al ready % 2 9 % 3 F . ▁ ▁If ▁the ▁form ▁is ▁processed ▁on ▁the ▁server ▁by ▁a ▁CG I ▁script , ▁the ▁script ▁may ▁typically ▁receive ▁the ▁query ▁string ▁as ▁an ▁environment ▁variable ▁named ▁Q U ERY _ STRING . ▁ ▁Track ing ▁ ▁A ▁program ▁receiving ▁a ▁query ▁string ▁can ▁ignore ▁part ▁or ▁all ▁of ▁it . ▁If ▁the ▁requested ▁URL ▁corresponds ▁to ▁a ▁file ▁and ▁not ▁to ▁a ▁program , ▁the ▁whole ▁query ▁string ▁is ▁ignored . ▁However , ▁regardless ▁of ▁whether ▁the ▁query ▁string ▁is ▁used ▁or ▁not , ▁the ▁whole ▁URL ▁including ▁it ▁is ▁stored ▁in ▁the ▁server ▁log ▁files . ▁ ▁These ▁facts ▁allow ▁query ▁strings ▁to ▁be ▁used ▁to ▁track ▁users ▁in ▁a ▁manner ▁similar ▁to ▁that ▁provided ▁by ▁HTTP ▁cookies . ▁For ▁this ▁to ▁work , ▁every ▁time ▁the ▁user ▁download s ▁a ▁page , ▁a ▁unique ▁identifier ▁must ▁be ▁chosen ▁and ▁added ▁as ▁a ▁query ▁string ▁to ▁the ▁URLs ▁of ▁all ▁links ▁the ▁page ▁contains . ▁As ▁soon ▁as ▁the ▁user ▁follows ▁one ▁of ▁these ▁links , ▁the ▁corresponding ▁URL ▁is ▁requested ▁to ▁the ▁server . ▁This ▁way , ▁the ▁download ▁of ▁this ▁page ▁is ▁linked ▁with ▁the ▁previous ▁one . ▁ ▁For ▁example , ▁when ▁a ▁web ▁page ▁containing ▁the ▁following ▁is ▁requested : ▁ ▁< a ▁href =" foo . html "> see ▁my ▁page ! </ a > ▁ ▁< a ▁href ="