The Saudi Arabian police have been rounding up "Hajj overstayers" - people who came into the country for the annual pilgrimage, and haven't left yet. Reportedly about 2,000 were detained and deported just in the vicinity of Mecca in the past couple of weeks. For the most part these people were so poor that they cashed in their return tickets in order to live, once they arrived in Saudi Arabia. The Saudis want them out because there's a tendency for them to drift into the criminal underworld, and because some may have ties to terrorists.
The Saudis have good reason to be worried about terrorism. For example, the official Saudi report on the 24 February attack on the Abqaiq petroleum installation greatly inflated the effectiveness of their security measures, and downplayed the effects of the attack, which seems to have caused much more damage than was reported (perhaps twice as much). While the Saudi security at Abqaiq was adequate, further investigation found sloppiness on the part of the security personnel, and opportunities that the terrorists could have taken, but didn't. So the Saudis are tightening up their counter-terrorism efforts, in case they are not as lucky the next time around.