UPDATE (22 August / 12:30 PM):
Malaysia Airlines, AirAsia and Malindo have issued statements regarding this. Their messages are to the effect of either asking passengers to arrive at the airport four hours before their flights, or to check in online.
ORIGINAL STORY (22 August / 11:37 AM):
Airports are one of the places where having internet connectivity is pretty much a necessity. Earlier today, the KL International Airport suffered disruptions to its internet connectivity, which hampered an important process.
Malaysia Airports announced via Twitter that this caused delays to the check-in process. As such, flyers are advised to reach the airport four hours before their flight, as well as check in to their flights online. This applies to flights from both terminals.
The internet connection at both KLIA and KLIA2 have since been restored. At the time of writing, only the Flight Information Display at KLIA2 is not yet fully functioning. As a result of the systems disruption, 20 flights have also been delayed.
If you have an upcoming flight, it may be a good idea to head to the airport a little earlier than you usually need to. You should also check in online if possible to avoid issues when checking in at the airport.