I'd suggest it's certainly not obvious over-enforcement.
Both kik names exist in the realm of software. There's an argument to be made for confusion.
As a public service, some toilet or compost bin manufacturer ought to start "violating" trademarks by naming toilets etc. after litigious companies. We'd all get a kik out of hearing them argue that database consumers are likely to confuse the Oracle database with the Oracle water closet. [EDIT: "Sure it's a CRUD app, but I'm more interested in Deletion than Retrieval!"]
Of course there are arguments to be made; lawyers are involved.
Confusion. Microsoft is very likely to prevail in the infringement lawsuit.
This matter has even already been litigated. Microsoft Windows is a valid trademark, Windows is not defensible.
Please see lindows aka linspire.
Oh yeah, it seems like M$ were on the verge of winning that appeal, and only discontinued (and paid Lindows a multiple of its annual profit) out of pity.
- The only thing you can say about a trademark dispute like this, given the information that's public, is that "it depends on the specific situation as well as the perception of a large enough user base who might get confused".
- Trademark owners can ask (or C&D demand) just about whatever they want. What they could actually force you to do in a court is far, far less than what they typically ask.