Hundreds of students were unable to appear for the computer-based Common Admission Test for the second day on Sunday, as authorities rescheduled the test for carrying out repairs at the laboratories where computers suffered virus attack that disrupted the first day of the test.

The CAT, being conducted through computers for 10 days from November 28 to December 7, got off on Saturday to a troubled start, with a computer virus attacking 24 of the 104 centres.

The authorities decided not to hold the test on Sunday at these affected centres.

The candidates who could not sit for the test have been notified, and the test for them was being rescheduled, said Prometric, an American firm entrusted with conducting the test for 2.41 lakh candidates seeking admission to the IIMs and a few other business education schools.

About 2,000 students could not appear for the test on Saturday due to the virus attack that affected the computers at 50 laboratories in the 24 centres.

“Exhaustive plans were developed and put in place well in advance of the start of the testing window. Unfortunately, the particular viruses and malware that attacked the test delivery system were not detected by the anti-virus software at the testing centres,” said Ramesh Nava, vice-president and general manager, Asia Pacific, Japan and Africa, Prometric.

Technicians were sent to address these problems, Prometric said.

“Candidates are our first and foremost priority, and Prometric is making every effort to provide all CAT aspirants an opportunity to test,” Mr. Nava said.

Prometric and the IIMs have made an announcement on the IIM-CAT websitethat the affected candidates would also be provided with new appointments within this year’s testing period.

However, there was confusion among students for whom the test has been rescheduled. “We were not informed immediately. When there is change in the schedule, we must be informed immediately. The change in the schedule adds to the pressure on us,” a student said.

Prometric said it generated new appointments for those who could not take the test, and they were being contacted through SMS and email.

The launch of the online CAT meant delivery of exams at more than 360 testing laboratories in 104 centres. “It is an ambitious project, but well within the means and experience of Prometric,” Prometric said.

The laboratories closed on Sunday include 11 in Bangalore, eight in Bhopal, six each in Lucknow and Mumbai, five in Delhi, four in Ghaziabad, two each in Varanasi and Hyderabad and one each in Bhubaneswar, Chandigarh, Nagpur, Kolkata and Coimbatore.