Custom vertex/fragment shader, renders box around point light at the edge of it's range. How can I fix this?

I wrote t$$anonymous$$s basic vertex/fragment shader. It's working all right except that it renders a box at the edge of any point light's range.

         //user defined vars
         uniform sampler2D _MainTex;
         uniform float4 _MainTex_ST;
         uniform float4 _Color;
         uniform float4 _SpecColor;
         uniform float _Gloss;
         //uniform float4 _RimColor;
         uniform float _S$$anonymous$$niness;
         //uniform float _RimPower;
         
         //unity defined vars
         uniform float4 _LightColor0;
         
         //base input structs
         struct vertexInput{
             float4 vertex : POSITION;
             float3 normal : NORMAL;
             float4 texcoord : TEXCOORD0;
         };
         
         struct vertexOutput{
             float4 pos : SV_POSITION;
             float4 tex : TEXCOORD0;
             float4 posWorld : TEXCOORD1;
             float3 normalDir : TEXCOORD2;
         };
         
         //vertex function
         
         vertexOutput vert(vertexInput v){
             vertexOutput o;
             
             o.posWorld = mul(_Object2World,v.vertex);
             o.normalDir = normalize( mul( float4( v.normal, 0.0), _World2Object ).xyz );
             o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
             o.tex = v.texcoord;
             
             return o;
         }
         
         //fragment function
         
         float4 frag(vertexOutput i) : COLOR {
             
             float3 normalDirection = i.normalDir;
             float3 viewDirection = normalize(_WorldSpaceCameraPos.xyz - i.posWorld.xyz );
             float3 lightDirection;
             float atten;
             float4 tex = tex2D(_MainTex, i.tex.xy * _MainTex_ST.xy + _MainTex_ST.zw);
             
             //START NEEDS TO BE OPTIMIZED!!
             if(_WorldSpaceLightPos0.w == 0.0){ //directional
                 atten = 1.0;
                 lightDirection = normalize(_WorldSpaceLightPos0.xyz);
             }
             else{
                 float3 fragmentToLightSource = _WorldSpaceLightPos0.xyz - i.posWorld.xyz;
                 float distance = length(fragmentToLightSource);
                 atten = 1.0/distance;
                 lightDirection = normalize(fragmentToLightSource);
             }
             //END NTBO
             
             float3 diffuseReflection = atten * _LightColor0.xyz * saturate( dot( normalDirection, lightDirection ) );
             float3 specularReflection = diffuseReflection * _SpecColor.xyz * _Gloss * pow( saturate ( dot ( reflect (-lightDirection, normalDirection ),viewDirection ) ),_S$$anonymous$$niness );
             
             //rim lighting
                 //float rim = 1 - saturate(dot(normalize(viewDirection),normalDirection));
                 //float3 rimLighting = saturate(dot(normalDirection,lightDirection)* _RimColor.xyz * _LightColor0.xyz * pow(rim,_RimPower));
         
             float3 lightFinal = UNITY_LIGHTMODEL_AMBIENT.xyz + diffuseReflection + specularReflection; //+ rimLighting;
             
             //Texture maps
             
             return float4 (tex.xyz * lightFinal * _Color.xyz,1.0);
         }            
         ENDCG
     }
     Pass{
         Tags{"LightMode" = "ForwardAdd"}
         Blend One One
         CGPROGRAM
         #pragma vertex vert
         #pragma fragment frag
         
         //user defined vars
         uniform sampler2D _MainTex;
         uniform float4 _MainTex_ST;
         uniform float4 _Color;
         uniform float4 _SpecColor;
         //uniform float4 _RimColor;
         uniform float _S$$anonymous$$niness;
         //uniform float _RimPower;
         uniform float _Gloss;
         
         //unity defined vars
         uniform float4 _LightColor0;
         
         //base input structs
         struct vertexInput{
             float4 vertex : POSITION;
             float3 normal : NORMAL;
             float4 texcoord : TEXCOORD0;
         };
         
         struct vertexOutput{
             float4 pos : SV_POSITION;
             float4 tex : TEXCOORD0;
             float4 posWorld : TEXCOORD1;
             float3 normalDir : TEXCOORD2;
         };
         
         //vertex function
         
         vertexOutput vert(vertexInput v){
             vertexOutput o;
             
             o.posWorld = mul(_Object2World,v.vertex);
             o.normalDir = normalize( mul( float4( v.normal, 0.0), _World2Object ).xyz );
             o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
             o.tex = v.texcoord;
             
             return o;
         }
         
         //fragment function
         
         float4 frag(vertexOutput i) : COLOR {
             
             float3 normalDirection = i.normalDir;
             float3 viewDirection = normalize(_WorldSpaceCameraPos.xyz - i.posWorld.xyz );
             float3 lightDirection;
             float atten;
             float4 tex = tex2D(_MainTex, i.tex.xy * _MainTex_ST.xy + _MainTex_ST.zw);    
             
             //START NEEDS TO BE OPTIMIZED!!
             if(_WorldSpaceLightPos0.w == 0.0){ //directional
                 atten = 1.0;
                 lightDirection = normalize(_WorldSpaceLightPos0.xyz);
             }
             else{
                 float3 fragmentToLightSource = _WorldSpaceLightPos0.xyz - i.posWorld.xyz;
                 float distance = length(fragmentToLightSource);
                 atten = 1.0/distance;
                 lightDirection = normalize(fragmentToLightSource);
             }
             //END NTBO
             
             float3 diffuseReflection = atten * _LightColor0.xyz * saturate( dot( normalDirection, lightDirection ) );
             float3 specularReflection = diffuseReflection * _SpecColor.xyz * _Gloss * pow( saturate ( dot ( reflect (-lightDirection, normalDirection ),viewDirection ) ),_S$$anonymous$$niness );
             
             //rim lighting
                 //float rim = 1 - saturate(dot(normalize(viewDirection),normalDirection));
                 //float3 rimLighting = saturate(dot(normalDirection,lightDirection)* _RimColor.xyz * _LightColor0.xyz * pow(rim,_RimPower));
             
             float3 lightFinal = diffuseReflection + specularReflection; //rimLighting;
                                                     
             return float4 (lightFinal,1.0);
         }            
         ENDCG
     }
     
 }

Can anyone point out where I'm going wrong?