Using underhanded tactics or lies to disparage another's product in the marketplace is subject to a civil suit.
By purposely breaking Opera on a site visited by millions, Microsoft tried to make those users with Opera think their browser was broken, casting doubt on the functionality and usability of that browser, which can be incentive for people to switch to a more "compatible" browser, such as IE. Such action is bad enough, but coming from a convicted monopolist known for anticompetitive behavior is that much worse.
While I'm not conceeding this was "underhanded", a lie, or disparaging, please post the specific causes of action and their authority.
By purposely breaking Opera
There was no "breaking" of anything.
Microsoft tried to make those users with Opera think their browser was broken, casting doubt on the functionality and usability of that browser, which can be incentive for people to switch to a more "compatible" browser, such as IE.
This is called marketing. Ever heard commercials with the term "other leading ____" where there is a distinct picture of something that looks like the other company's product? Besides, Opera users are virtually by definition power users (computer novices don't know anything about Opera and don't download it; they use IE), even the below average Opera user knows exactly what is going on here and that it is limited to certain sites.
Such action is bad enough, but coming from a convicted monopolist known for anticompetitive behavior is that much worse.
Microsoft was never "convicted" of anything that I know of.
Dude, there are a LOT of reasons to diss MS. Some of their products are crappy and buggy (Word); they have licensing agreements that are driving many users to other options; they discontinue support of older apps, effectively forcing upgrades by people and companies that don't really want to upgrade; and their technical support has individuals that are less knowlegable than the average computer power user. I guarantee you I know more Word that 90% of the Word tech support people. I have never, ever, gotten a helpful response from Microsoft support.
But making things up by saying stuff like this is illegal makes you, not Microsoft, look silly. If you want to use this as a reason to not purchase MS products, and encourage others to follow, go for it. I might actually support you. But saying this stuff is illegal is ridiculous.