The Pope is declaring a 'holy war' against people who claim falsely that the Virgin Mary is appearing to them.
He will attempt to snuff out an explosion of bogus heavenly apparitions with new guidelines to help bishops root out frauds.
...In some cases exorcists will be used to determine if a credible apparition is 'divine' origin or 'demonic'.
Thus far, most Marian apparitions have not been decided on by the Church. According to The Marian Library/International Marian Research Institute:
During the twentieth century, there have been 386 cases of Marian apparitions. The Church has made "no decision" about the supernatural character regarding 299 of the 386 cases. The Church has made a "negative decision" about the supernatural character in seventy-nine of the 386 cases. Out of the 386 apparitions, the Church has decided that "yes" there is a supernatural character only in eight cases: Fatima (Portugal), Beauraing (Belgium), Banneux (Belgium), Akita (Japan), Syracuse (Italy), Zeitoun (Egypt), Manila (Philippines) (according to some sources), and Betania (Venezuela). Local bishops have approved of the faith expression at the sites where these eight apparitions occurred. Besides the eight approved apparitions, there have been eleven (out of the 386 apparitions) which have not been approved with a "supernatural character," but which have received a "yes" to indicate the local bishop's "approval of faith expression (prayer and devotion) at the site." (link)
That is approximately 77% Undecided, 2% Yes, 20% No. I believe that the laity is free to believe or not believe any of these types of private revelations.
I thought the graph on this page was interesting. Looking at the past, the Middle ages saw a boom in Marian apparitions while the early church years has no recorded sightings:
Patristic Age : There is no recorded literature about apparitions for the early centuries of the Church. The first attestations of Marian apparitions are from the fourth century. For example, Gregory of Nyssa, who lived in the fourth century, recorded that Gregory the Wonder worker (213-270 A.D.) was the first beneficiary of a Marian apparition.
This page gives some of the guidelines for judging these events. A change in canon law in 1969 loosened the regulations on new occurrences:
A new era opened in the canonical regulations dealing with apparitions occurred in 1969. In that year, Pope Paul VI deleted certain canons of the Code of Canon Law (1917). These canons had specifically forbidden the publication of all books or pamphlets about new apparitions, revelations, visions, prophecies, and miracles, or which introduce new devotions, even though justified as private. Such prohibitions are not part of the Code of Canon Law (1983). So the many reports of Marian apparitions may in part be due to the new freedom to discuss freely and to report such occurrences to the media, without first submitting them to ecclesiastical approbation.