Technical glitches that disrupted the first on-line Common Admission Test for entry to the Indian Institutes of Management and top business schools at one-fifth of the exam centres were blamed on a virus attack, as the snag prevented hundreds of students to take the exam for the second day on Sunday.

Authorities rescheduled the test at 24 of the 104 Centres across the country to fix the glitches affecting more students. About 2,000 students could not appear in the test on Saturday due to the virus that swamped the computers at about 50 labs in the 24 centres.

CAT, being conducted through computers for a period of 10 days from November 28 to December 7, got off to a troubled start on Saturday after which the authorities decided not to hold the test at these affected centres.

Candidates, who could not appear the test, have been notified and their tests are currently being rescheduled within the testing period, said Prometric, the American firm entrusted with the task of conducting the tests for around 2.41 lakh candidates for admission to the IIMs and a few other B-schools.

"Exhaustive plans were developed and put in place well in advance of the start of the testing window. Unfortunately, the particular viruses and malware (malicious software) 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 have been dispatched to address these isolated problems, Prometric said.