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."

The broader distribution of MSE to consumers might not be as welcome. When Ed Bott at ZDNet asked Symantec and McAfee their thoughts, their stance was much the same as it is was before: "Microsoft's software offers only basic protection; ours is so much better, people really should use it." Infoworld is reporting that Trend Micro might not be so conciliatory.

Speaking to Infoworld, Carol Carpenter, the general manager of the consumer and small business group at Trend Micro said, "Commercializing Windows Update to distribute other software applications raises significant questions about unfair competition." She continued, "Windows Update is a de facto extension of Windows, so to begin delivering software tied to updates has us concerned. Windows Update is not a choice for users, and we believe it should not be used this way."

Trend Micro's response shows a poor understanding of the action Microsoft has taken. MSE is being offered not through Windows Update, but through the related Microsoft Update service. Microsoft Update, which updates a broad range of Microsoft products and occasionally offers new ones, requires a deliberate opt-in: it isn't enabled by default. Moreover, MSE will only be offered to customers who do not have an existing antivirus product installed—and in any case is offered as an optional download.

Though an antirust suit over an optional download that is only offered after enabling an optional feature seems unlikely, that competitors would even raise such concerns shows Microsoft's uniquely peculiar position in the industry. The third-party software vendors are more than happy to insist that Windows needs antivirus software and that using a Windows machine without such software is dangerous—but if Microsoft agrees with their assessment and tries to improve the situation itself, they threaten to cry foul.