Microsoft placed on inclusion in the Referral Server, the IAPs would have had no reason to limit the percentage of subscribers that used one particular browser or another. As Cameron Myhrvold explained to colleagues within Microsoft in April 1997, "ISPs are agnostic on the browser. It is against their nature to favor a browser or even a platform. This has been damn hard for us to influence." In fact, Myhrvold told the same colleagues that he "had a hard time guiding the ISPs to IE loyalty even when I make them sign explicit terms and conditions in a legal contract." 264.  Microsoft monitored the extent of compliance of IAPs in the Referral Server with the shipment restrictions contained in their agreements. It did this by periodically asking each of the ten IAPs to send Microsoft estimates of the number of copies of Internet Explorer ? and non-Microsoft browsing software ? they were shipping. When, from time to time, various IAPs in the Windows 95 Referral Server (specifically Netcom, Concentric, and EarthLink) fell below the shipment quotas specified in their agreements with Microsoft, executives at Microsoft reacted by contacting the derelict companies and urging them to meet their obligations. Concentric and Earthlink eventually (by May 1998, if not sooner) reduced their Navigator shipments enough to bring them below the required percentage. Microsoft never formally removed an IAP from the Referral Server. For a time after the release of Internet Explorer 4.0, however, no entry for Netcom appeared in the new version