On Monday, its own news portal "Vatican News", which reports on events in the Vatican in 37 languages, was unavailable for some time.
Last week, the Vatican website vatican.va had already gone offline for days.
The website contains information on Vatican institutions, the Pope's appointments and daily official announcements, for example on personalities in the universal church.
Vatican spokesman Matteo Bruni referred at the weekend to an "abnormal number of interactions" with the Vatican domain.
The countermeasures introduced included access restrictions and, in combination with the unusual interactions, led to the current problems.
Some media speculated about a possible connection with the Vatican visit of the Ukrainian First Lady Olena Selenska last Wednesday.