The malfunction initially affected 13 CTX machines, but AoT officials' decision to change the uninterruptible power supply (UPS) devices in an attempt to get the systems running again resulted in just six of the 26 CTX machines functioning.

Acting Airports of Thailand (AoT) managing director Kalaya Pakakong said the scanning system breakdown was due to damage caused by a computer virus and AoT had so far repaired 16 machines.

Admiral Bannawit Kengrian, head of the National Legislative Assembly committee investigating problems at Suvarnabhumi Airport and advisor to the AoT chairman, said the committee would today inspect the taxiways, runways and the failed CTX machines.

Assistant Army chief Gen Saprang Kalayanamitr, the AoT board chairman, said he had ordered officials to identify the cause of the failure and to initiate a long-term plan to prevent a similar problem occurring again.

An informed source said the initial investigation found that AoT officials manning the CTX machines in the passenger terminal's eastern wing had put other programs into the computer supervising the scanners. This had caused a virus to affect the server and eventually caused the breakdown.

AoT had to bring in 100 military personnel to help carry passengers' baggage.

US technicians from GE InVision Inc, which supplied the 26 CTX machines, were called in to repair the machines, the source said.