Code:

type

PTOKEN_GROUPS = TOKEN_GROUPS^;

function RunningAsAdministrator(): Boolean;

var

SystemSidAuthority: SID_IDENTIFIER_AUTHORITY = SECURITY_NT_AUTHORITY;

psidAdmin: PSID;

ptg: PTOKEN_GROUPS = nil;

htkThread: Integer; { HANDLE }

cbTokenGroups: Longint; { DWORD }

iGroup: Longint; { DWORD }

bAdmin: Boolean;

begin

Result := false;

if not OpenThreadToken(GetCurrentThread(), // get security token

   TOKEN_QUERY, FALSE, htkThread) then

   if GetLastError() = ERROR_NO_TOKEN then

   begin

     if not OpenProcessToken(GetCurrentProcess(),

       TOKEN_QUERY, htkThread) then

       Exit;

   end

   else

     Exit;

if GetTokenInformation(htkThread, // get #of groups

   TokenGroups, nil, 0, cbTokenGroups) then

   Exit;

if GetLastError() <> ERROR_INSUFFICIENT_BUFFER then

   Exit;

ptg := PTOKEN_GROUPS(getmem(cbTokenGroups));

if not Assigned(ptg) then

   Exit;

if not GetTokenInformation(htkThread, // get groups

   TokenGroups, ptg, cbTokenGroups, cbTokenGroups) then

   Exit;

if not AllocateAndInitializeSid(SystemSidAuthority,

   2, SECURITY_BUILTIN_DOMAIN_RID, DOMAIN_ALIAS_RID_ADMINS,

   0, 0, 0, 0, 0, 0, psidAdmin) then

   Exit;

iGroup := 0;

while iGroup < ptg^.GroupCount do // check administrator group

begin

   if EqualSid(ptg^.Groups[iGroup].Sid, psidAdmin) then

   begin

     Result := TRUE;

     break;

   end;

   Inc(iGroup);

end;

FreeSid(psidAdmin);

end;