|installstub.exe is a part of Plaxo Toolbar software.
"In Plaxo Toolbars for Outlook and Outlook Express version 2.4.x, the process installstub.exe is Plaxo's core executable program, which is used to check for new or updated information (e.g. bug fixes) from the Plaxo Network. This process has been renamed to "PlaxoHelper.exe" in later versions. InstallStub (or PlaxoHelper) is also responsible for attaching Plaxo to Outlook Express when it starts up, since Outlook Express has no API.
When your contacts reply to an Update Request, the updated information is returned to Plaxo's servers. Installstub.exe or PlaxoHelper.exe ensure that your Outlook or Outlook Express address book is synchronized with the Plaxo servers.
If you use a personal firewall, such as ZoneAlarm, you should allow InstallStub or PlaxoHelper.exe to access the Internet so that Plaxo will function properly."