Whats wrong with my filesystem watcher code VB.NET? - vb.net

Question

when my file system watcher detects a virus a dialog shows but when i click the delete file option it says its open in my program but in the filesystem watcher when i add the openfiledialog.Dispose function it doesnt show my dialog so heres the code can somone provide a fix? code below.
Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
Try
Detect.Labellastreal.Text = e.FullPath
ListBox3.Items.Add(Detect.Labellastreal.Text)
Me.OpenFileDialog3.FileName = ""
Dim scanbox As New TextBox
scanbox.Text = My.Computer.FileSystem.ReadAllText(Application.StartupPath & "\VirusList.dat").ToString
Dim md5 As New MD5CryptoServiceProvider
Dim f As New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, &H2000)
f = New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, &H2000)
md5.ComputeHash(f)
Dim hash As Byte() = md5.Hash
Dim buff As New StringBuilder
Dim hashByte As Byte
For Each hashByte In hash
buff.Append(String.Format("{0:X2}", hashByte))
Next
f.Close()
If scanbox.Text.Contains(buff.ToString) Then
Me.OpenFileDialog3.FileName = e.FullPath
Detect.ShowDialog()
WriteToLog("Virus detected")
End If
Catch exception1 As Exception
ProjectData.SetProjectError(exception1)
Dim ex As Exception = exception1
ProjectData.ClearProjectError()
End Try
End Sub

Answer 1

Firstly, don't even bother using that code. FileSystemWatcher is unreliable, and fails lots of the time.
Secondly, remove f = New FileStream(e.FullPath, FileMode.Open, FileAccess.Read, FileShare.Read, &H2000), as you're calling it twice.
Lastly, for a Visual Basic anti-virus with real-time protection, I recommend you use this code:
Private Function GetMD5String(ByVal strFilename As String) As String
Dim MD5 As String = GetMD5String(strFilename)
Dim cMD5 = Security.Cryptography.MD5.Create
Dim bytHash As Byte()
Dim sb As New System.Text.StringBuilder
Dim scanbox As New TextBox
scanbox.Text = My.Computer.FileSystem.ReadAllText("viruslist.txt").ToString
Me.OpenFileDialog1.FileName = strFilename
Using cStream As New IO.FileStream(strFilename, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read)
bytHash = cMD5.ComputeHash(cStream)
End Using
For Each c In bytHash
sb.Append(c.ToString("X2"))
Next
If scanbox.Text.Contains(sb.ToString) Then
Detect.ShowDialog()
WriteToLog("Malicious exploit detected.")
Quarantinevb.ListBox1.Items.Add(strFilename)
End If
Return sb.ToString
End Function
Works well and is reliable.