Microsoft have published a full list of guidelines to help Internet Explorer add-on developers create quality add-ons. These guidelines to respond to demand from the developer community and to help share the thinking of the IE team, gathered from years of providing support to users and developers. Its strongly recommend that developers follow these guidelines when developing add-ons for IE users. “We occasionally come across add-ons that violate these guidelines so egregiously that we treat them as malware; on the other hand, we frequently see really helpful and creative add-ons that put the “user in control” and enhance the browsing experience,” announced IE blog.
More info: KB973764