Every once in a while I get about 10 - 20 identical errors on my asp.net app.  It's always the same, and I'm wondering if it is someone trying to hack in (it happens about once a month).
  Source: System.Web
  
  Message: The file '/~/Default.aspx' does not exist.
  
  User IP: 89.122.29.80
  
  User Browser: Unknown 0.0
  
  User OS: Unknown
  
  Stack trace:    at
  System.Web.UI.Util.CheckVirtualFileExists(VirtualPath
  virtualPath)  at
  System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath
  virtualPath, Boolean noBuild, Boolean
  allowCrossApp, Boolean
  allowBuildInPrecompile)  at
  System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext
  context, VirtualPath virtualPath,
  Boolean noBuild, Boolean
  allowCrossApp, Boolean
  allowBuildInPrecompile)  at
  System.Web.Compilation.BuildManager.GetVirtualPathObjectFactory(VirtualPath
  virtualPath, HttpContext context,
  Boolean allowCrossApp, Boolean
  noAssert)  at
  System.Web.Compilation.BuildManager.CreateInstanceFromVirtualPath(VirtualPath
  virtualPath, Type requiredBaseType,
  HttpContext context, Boolean
  allowCrossApp, Boolean noAssert)  at
  System.Web.UI.PageHandlerFactory.GetHandlerHelper(HttpContext
  context, String requestType,
  VirtualPath virtualPath, String
  physicalPath)  at
  System.Web.UI.PageHandlerFactory.System.Web.IHttpHandlerFactory2.GetHandler(HttpContext
  context, String requestType,
  VirtualPath virtualPath, String
  physicalPath)  at
  System.Web.HttpApplication.MapHttpHandler(HttpContext
  context, String requestType,
  VirtualPath path, String
  pathTranslated, Boolean useAppConfig) 
  at
  System.Web.HttpApplication.MapHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at
  System.Web.HttpApplication.ExecuteStep(IExecutionStep
  step, Boolean completedSynchronously)
why on earth would someone be trying to access "/~/Default.aspx" ?