Investigators looking into the financial collapse in Cyprus say key data about Greek bond purchases is missing from the country's biggest lender.

A report by professional services firm Alvarez & Marsal said a "mass deletion of data" had been found on one computer.

The missing data relates to Greek bonds the bank purchased, which turned into losses of almost $2.5 billion during the Greek debt crisis.

"Based on an initial review of the data, our computer forensic technologists have found that the computers of two employees ... have had wiping software loaded which is not part of the standard software installations at the Bank of Cyprus," the report said.

It is not clear yet whether the wiping of records was accidental or deliberate.

The report says the bank was not in breach of regulatory limits, despite a high concentration of Greek debt.

But it said there was early regulatory concern about the bank's exposure to Greek government bonds.

"The [central bank] formally requested information regarding [Bank of Cyprus's] holdings of [Greek bonds] in March 2010, however, no written response was received," the report said.

It added that the central bank did not follow up on the lack of a written response in a timely way and the reason for that was unclear.

The investigation pre-dates the bailout agreed for Cyprus last month, which will see hefty levies imposed on deposits at the bank of more than $125,000.

ABC/Reuters