Spyware. its comin something security alert ("Warning Spyware activities Detected")i use avast but

Question

its comin something security alert ("Warning Spyware activities Detected")i use avast but when i scan it .it shows no spyware and there is also a win32 bho-kd trj ("C:/windows/system32/diges.dll)but i cannot delete it please helpXP user