Bing is Microsoft's search engine answer to Google. Like all things Microsoft touches these days, it is inferior in quality. It just isn't a good search engine. Its results are less often what you want and are hard to use.
In addition to being an inferior search engine to Google, Bing is aggressive to an almost malware degree. When you start up a new system and use Internet Explorer, the Bing software is very insistant on taking a prominent place in your system until you root it out and remove it, even if you have no interest is using it. It shows up on your screen when you don't ask it to, it installs itself, it makes itself hard to ignore when it appears on the screen. When I bought my wife a new computer recently, one of my first acts was to devote the roughly 45 minutes that was required to remove Bing from her system.
I have yet to meet a satisfied Bing customer.
Apparently, Bing also systematically uses information gathered from users who make Google searches while it is installed, effectively acting as spyware, to reverse engineer Google's search engine tricks.
While I have no problem, in general, with reverse engineering other people's technology that doesn't have formal legal intellectual property protection, and there are far more harmful ends to which information gathered with spyware can be put, I still am not happy about any software that secretly enlists millions of users into a program of mass information sharing for undisclosed reasons. I don't think that Google has any legitimate legal grievance against Microsoft for this conduct, but I also don't think that it is appropriate for Microsoft as a legitimate software company to be inserting software so close to malware and spyware into people's computers while passing off what they are doing as offering the same kind of far less intrusive service as Google and Yahoo.
Indeed, perhaps the most appropriate response would be for major Internet Security firms like Norton, AVG and McAfee to decide to classify it as a security threat and automatically prompt users to remove it from their systems with a description of Bing's defects similar to that made available to explain the threat caused by other security threats it flags from tracking cookies ot phishing websites to trojans. These companies aren't required to determine that software is illegal. They are simply in the business of identifying stuff on your computer or the Internet that you don't want. Malware status is a matter of opinion, so long as the basis of that classification is disclosed, and these companies would be well within their rights to classify Bing as malware based on what it does.