To make sure or certain; insure: Our precautions ensured our safety.
Also see [link|http://dictionary.reference.com/search?q=assure|Assure]:
Usage Note: Assure, ensure, and insure all mean \ufffdto make secure or certain.\ufffd Only assure is used with reference to a person in the sense of \ufffdto set the mind at rest\ufffd: assured the leader of his loyalty. Although ensure and insure are generally interchangeable, only insure is now widely used in American English in the commercial sense of \ufffdto guarantee persons or property against risk.\ufffd
I too would have used ensure rather than insure in Alex's title - it has a slightly different connotation to me than insure. MS isn't buying a policy.
Cheers,
Scott.