Ars Technica posted a news story that Trend Micro is not happy that Microsoft is distributing Microsoft Security Essentials over Windows Update

In recent months, Microsoft has made a couple of moves to make its Microsoft Security Essentials antivirus software more widely used. First, the company relaxed licensing restrictions, making it permissible to use MSE in businesses with ten or fewer PCs; prior to this change, the software was only licensed for home users. Now, the company has started to distribute the software through its Microsoft Update distribution system.

Last month Ars asked antivirus vendors their thoughts about the expansion of MSE into small businesses. Their responses could best be summed up as "it's good that Microsoft is raising awareness of computer security, but our software is still much better."

Trend Micro cries antitrust over Microsoft Security Essentials