Microsoft is making moves to combat misleading ads which could also deliver malware and misleading downloads to users. From June 1, 2015, Microsoft will enforce the new evaluation criteria. Here's examples of what it classes as misleading ads, and a more details about the new warning for users in IE when SmartScreen is turned on.
Advertisements: The advertisement should not mislead you into visiting another site or downloading files.
Advertisements shown to a user:
Must not mislead or deceive, or confuse with the intent to mislead or deceive
Must be distinguishable from website content
Must not contain malicious code
Must not invoke a file download
Enforcing our criteria
When SmartScreen Filter is turned on, Internet Explorer will notify you about sites that contain an advertisement that is detected under our evaluation criteria. The warning will look like the following example:
We are currently updating our evaluation criteria to address new technology changes, industry trends, customer feedback, and our desire to help better protect our customers. We are working with the industry and our partners to understand and implement these changes. Microsoft Taking a Hard Stance Against Misleading and Malicious Advertisements