First Sergey thought they were common stalkers sticking in group. Then, however, something alerted him in their behavior only to make him instantly lie down holding the gun in front of him. A shout didn’t have any effect – these two failed to react in any way. When they came up closer, he had no single doubts remaining – the non-coordinated movements, rambling murmur, dragging feet. He faced zombied stalkers.
Sergey didn’t want to approach them fearing to recognize someone out of his friends missing in the Zone. He fired several times preventing the zombie from opening fire in response...
Those who suffered extensive impact of radiators in Yantar or some other sectors. Incautious stalkers quickly become insane, turning into walking semi-corpses. They are plentiful in the Zone, some can even reach the perimeter.
This way or another, it is impossible to help them: the process of personality erasure is irreversible. Although zombied stalkers can still use their weapons, they are rather stupid. Encountering them you can hear them murmuring bits of phrases which, though, are fully meaningless. In time zombied stalkers completely lose all the previous skills and turn into zombies.
As a rule, they are very aggressive and pose serious threat when in masses.
Poor souls subjected to prolonged exposure in Yantar and a few other heavily radiated sectors. Careless stalkers gone mad and turned into walking corpses. Many such corpses wander the Zone, some wander as far as the perimeter. They are beyond help because the destructive process is irreversible. Zombified stalkers are still able to use their weapons, but they are quite dumb and can be heard mumbling meaningless, fragmented sentences to themselves. They gradually lose all their skills and turn into zombies. They are usually very aggressive and can present a serious threat in large numbers.
Although they may be zombies, they are actually quite capable with weapons and can pose a threat, even when you're just facing a couple of them. They also seem to be tougher than their normal, human counterparts and can take quite a number of bullets before going down. Furthermore, they haven't forgotten the dangers of grenades, and if you toss one in their direction they may sprint away as if they were still sane - I personally consider this behaviour a bug.
Locations
Zombified Stalkers can be found in the Wild Territory, Yantar, Red Forest along with the X16 lab and the tunnels below; you may even run across a few in Pripyat.