Microsoft Corp. has given developers three months to conform with its tough new criteria for classifying programs as adware or risk having their programs blocked by its security products such as Windows Defender.

Microsoft will begin blocking adware programs beginning July 1. In the past, adware programs were allowed to run until users chose one of the recommended actions offered by the company's security software.

Microsoft re-evaluated its criteria for classifying applications as adware based on the principle that users should be able to choose and control what happens on their computers, said Michael Johnson, a member of the Microsoft Malware Protection Center.

Johnson said only programs displaying ads promoting goods and services inside other programs such as browsers will be evaluated as possible unwanted adware applications. He noted that if the program shows advertisements within its own borders it will not be assessed any further.

To avoid being flagged as adware and blocked, programs that include advertising must only display ads or groups of ads that have an obvious close button. The ads must also clearly indicate the name of the program that generated them.

Recommended methods for closing the ad include an "X" or the word "close" in a corner. The program name can be specified with phrases such as "Ads by ...",  "Powered by ...", "This ad served by ..." or "This ad is from ...".

"Using abbreviations or company logos alone are not considered clear enough," Johnson said. "Also, only using 'Ads not by this site' does not meet our criteria, because the user does not know which program created the ad."

Programs also need to provide a standard uninstall method in the Windows control panel or the browser add-on management interface if the program operates as a browser extension or toolbar. The corresponding uninstall entries must contain the same program names as displayed in the generated ads.