在WIN32下用DELPHI侦测目录变化，可用WIN32提供的文件改变通知API来完成。FindFirstChangeNotification, FindNextChangeNotification，FindCloseChangeNotification。
在应用程序中调用这些函数时，产生一个监控这个变化的句柄，可用WAIT函数集来等待这个变化。这样，当监控程序运行时，可以达到监控文件变化的动作。更进一步，可把此程序做成一个状态区图标（TRAY）来完成监控。

Windows在删除、复制、移动、访问文件时并不发送消息，当然截获不到。要截取这些操作过程的唯一办法就是截获API，这又需要你编写Vxd程序了，杀毒软件都是这样作的。你注意一下杀毒软件一般都带有一个vxd程序。光有vxd还不行，还需截获文件API。还有另外一个办法，就是CIH病毒采用的办法，直接跳到系统零层去操作。具体办法如下：
一、SIDT指令（ 将中断描述符表寄存器IDTR－－64位宽，16～47Bit存有中断描述符表IDT基地址－－的内容存入指定地址单元）不是特权指令，就是说我们可以在Ring3下执行该指令，获得IDT的基地址，从而修改IDT，增加一个中断门安置我们的中断服务，一旦Ring3程序中产生此中断，VMM就会调用此中断服务程序，而此中断服务程序就运行在Ring0下了。这一点与在DOS下非常相似。

二、要实现对系统中所有文件I/O操作的实时监视，还要用到另一种关键技－FileHooking，通过挂接一个处理函数，截获所有与文件I/O操作有关的系 统调用。Windows9x使用32位保护模式可安装文件系统(IFS)，由可安装文件系统管理器(IFSManager)协调对文件系统和设备的访问，它接收以Win32API函数调用形式向系统发出的文件I/O请求，再将请求转给文件系统驱动程序FSD，由它调用低级别的IOS系统实现最终访问。每个文件I/OAPI调用都有一个特定的FSD函数与之对应，IFSManager负责完成由API到FSD的参数装配工作，在完成文件I/OAPI函数参数的装配之后转相应FSD执行之前，它会调用一个称为FileSystemApiHookFunction的Hooker函数。通过安装自己的Hooker函数，就可以截获系统内所有对文件I/O的API调用，从而实现实时监控。
=========================================
procedure TForm1.Button2Click(Sender: TObject);
begin
  {establish a notification for file name changes on the selected directory}
  NotificationHandle := FindFirstChangeNotification(PChar(DirectoryListBox1.Directory), FALSE,FILE_NOTIFY_CHANGE_FILE_NAME);
  {if the notification was set up correctly, modify some UI elements...}
  if (NotificationHandle <> INVALID_HANDLE_VALUE) then
  begin
    Button1.Enabled := TRUE;
    Button2.Enabled := FALSE;
  end
  else
  begin
    {...otherwise indicate that there was an error}
    ShowMessage('There was an error setting the notification');
    Exit;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  dwResult: DWORD;         // holds the result of waiting on the notification
  Waiting: Boolean;        // loop control variable
begin
  {setup the loop control for a continuous loop}
  Waiting := TRUE;
  {indicate that the application is waiting for the change notification to fire}
  Button1.Enabled := FALSE;
  StatusBar1.SimpleText := 'Now waiting for a filename change';
  Application.ProcessMessages;
  {enter the loop}
  while Waiting do
  begin
    {at this point, the application is suspended until the notification
     object is signaled that a filename change has occured in the
     selected directory (this includes file deletions)}
    dwResult := WaitForSingleObject(NotificationHandle,INFINITE);
    if (dwResult = WAIT_OBJECT_0) then

    begin
      {indicate that the notification object was signaled}
      ShowMessage('The selected directory signaled a filename change');

      {query the user to see if they wish to continue monitoring this
       directory}
      if Application.MessageBox('Do you wish to continue monitoring this directory?', 'Continue?', MB_ICONQUESTION or
                                MB_YESNO) = IDYES then

        {if the user wishes to continue monitoring the directory, reset
         the notification object and continue the loop...}
        FindNextChangeNotification(NotificationHandle)
      else
        {...otherwise break out of the loop}
        Waiting := FALSE;
    end;
  end;

  {close the notification object}
  FindCloseChangeNotification(NotificationHandle);

  {reset UI elements}

  Button1.Enabled := FALSE;
  Button2.Enabled := TRUE;
  StatusBar1.SimpleText := '';
  FileListBox1.Update;
end;
===========================================
下面是一个监视的控件：
unit dirnotify;

interface

uses
  Windows, Messages, SysUtils, Classes,
  Graphics, Controls, Forms, Dialogs;

type
  EDirNotificationError = class(Exception);

  TDirNotify = class;
  TNotifyFilter = (nfFileName, nfDirName, nfAttributes, nfSize, nfLastWrite,
    nfSecurity);
  TNotifyFilters = set of TNotifyFilter;

  TNotificationThread = class(TThread)
    Owner: TDirNotify;
    procedure Execute; override;
    procedure DoChange;
  end;

  TDirNotify = class(TComponent)
  private
    FEnabled: Boolean;
    FOnChange: TNotifyEvent;
    FNotificationThread: TNotificationThread;
    FPath: String;
    FWatchSubTree: Boolean;
    FFilter: TNotifyFilters;

    procedure SetEnabled( Value: Boolean );
    procedure SetOnChange( Value: TNotifyEvent );
    procedure SetPath( Value: String );
    procedure SetWatchSubTree( Value: Boolean );
    procedure SetFilter( Value: TNotifyFilters );

    procedure RecreateThread;

  protected
    procedure Change;
    procedure Loaded; override;

  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;

  published
    property Enabled: Boolean read FEnabled write SetEnabled default True;
    property OnChange: TNotifyEvent read FOnChange write SetOnChange;
    property Path: String read FPath write SetPath;
    property WatchSubTree: Boolean read FWatchSubTree write SetWatchSubTree;
    property Filter: TNotifyFilters read FFilter write SetFilter default [nfFileName, nfDirName, nfAttributes, nfLastWrite, nfSecurity];
  end;


procedure Register;

implementation

const
  LASTERRORTEXTLENGTH = 500;

var
  LastErrorText: array [0..LASTERRORTEXTLENGTH] of char;


function GetLastErrorText: PChar;
begin
  FormatMessage( FORMAT_MESSAGE_FROM_SYSTEM,
    nil, GetLastError, 0, LastErrorText, LASTERRORTEXTLENGTH, nil );
  Result := LastErrorText;
end;


procedure TNotificationThread.Execute;
var
  h: THandle;
  nf: Longint;
  wst: LongBool;
begin
  nf := 0;
  if (nfFileName in Owner.Filter) then nf := FILE_NOTIFY_CHANGE_FILE_NAME;
  if (nfDirName in Owner.Filter) then nf := nf or FILE_NOTIFY_CHANGE_DIR_NAME;
  if (nfAttributes in Owner.Filter) then nf := nf or FILE_NOTIFY_CHANGE_ATTRIBUTES;
  if (nfSize in Owner.Filter) then nf := nf or FILE_NOTIFY_CHANGE_SIZE;
  if (nfLastWrite in Owner.Filter) then nf := nf or FILE_NOTIFY_CHANGE_LAST_WRITE;
  if (nfSecurity in Owner.Filter) then nf := nf or FILE_NOTIFY_CHANGE_SECURITY;

  // yeahh, this one is stupid but Win98 malfunctions in any other value than 0 or 1
  if Owner.FWatchSubTree then wst := Longbool(1)
  else wst := Longbool(0);

  h := FindFirstChangeNotification( Pointer(Owner.Path), wst, nf );
  if (h = INVALID_HANDLE_VALUE) then
    raise EDirNotificationError.Create( GetLastErrorText );

  repeat
    if (WaitForSingleObject( h, 1000 ) = WAIT_OBJECT_0) then
    begin
      Synchronize(DoChange);

      if not FindNextChangeNotification( h ) then
        raise EDirNotificationError.Create( GetLastErrorText );
    end;
  until Terminated;
end;


procedure TNotificationThread.DoChange;
begin
   Owner.Change;
end;


constructor TDirNotify.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);

  FEnabled := True;
  FFilter := [nfFileName];
end;


destructor TDirNotify.Destroy;
begin
  FNotificationThread.Free;
  inherited Destroy;
end;

procedure TDirNotify.Loaded;
begin
  inherited;

  RecreateThread;
end;


procedure TDirNotify.SetEnabled(Value: Boolean);
begin
  if Value <> FEnabled then
  begin
    FEnabled := Value;

    RecreateThread;
  end;
end;


procedure TDirNotify.SetPath( Value: String );
begin
  if Value <> FPath then
  begin
    FPath := Value;
    RecreateThread;
  end;
end;


procedure TDirNotify.SetWatchSubTree( Value: Boolean );
begin
  if Value <> FWatchSubTree then
  begin
    FWatchSubTree := Value;
    RecreateThread;
  end;
end;


procedure TDirNotify.SetFilter( Value: TNotifyFilters );
begin
  if Value <> FFilter then
  begin
    FFilter := Value;
    RecreateThread;
  end;
end;


procedure TDirNotify.SetOnChange(Value: TNotifyEvent);
begin
   FOnChange := Value;
end;


procedure TDirNotify.Change;
begin
   if Assigned(FOnChange) then
      FOnChange(Self);
end;


procedure TDirNotify.RecreateThread;
begin
  // destroy thread
  FNotificationThread.Free;
  FNotificationThread := nil;

  if FEnabled and not(csDesigning in ComponentState)
    and not(csLoading in ComponentState) and (FPath <> '') then
  begin
    // create thread
    FNotificationThread := TNotificationThread.Create(True);
    FNotificationThread.Owner := self;
    FNotificationThread.Resume;
  end;
end;


procedure Register;
begin
   RegisterComponents('System', [TDirNotify]);
end;

end.