Fearful that the office of its minister was being bugged, the finance ministry had instructed the Central Board of Direct Taxes ( CBDT) to use the secret funds of Income Tax investigation to engage a private agency to conduct a debugging operation after it was found that none of the revenue intelligence agencies under the FM had the wherewithal.

The finance ministry has under its arm the Central Economic Intelligence Bureau, I-T Investigation, Directorate of Revenue Intelligence and the Enforcement Directorate all, except for CEIB, having state-of-the-art equipment to intercept phone calls.

A private agency was hired to do the operation in the offices of FM and his close aides. Immediately after the operation, the FM's office removed the usual cleaners and housekeeping staff responsible for changing flowerpots, fearing that Intelligence Bureau (IB), under the home ministry, might have been using them to plant bugs in table corners or on flower vases.

During his interaction with a group of editors on Wednesday, Prime Minister Manmohan Singh said that the intelligence bureau had conducted an investigation on a "need to know" basis and reported that no bugging had taken place. He indirectly confirmed that home minister P Chidambaram may not have known of the probe.

"I asked the IB to do a thorough check. The IB reported back to me that there was nothing of the sort," the PM said.

A former joint director of the Intelligence Bureau, who was representing the private agency hired by the FM for debugging operation, S K Gupta, told Times Now that he had identified 16 spots where bugs may have been pasted.

"I was called in last September by senior finance ministry officials to carry out a security audit. I found 16 off white adhesives in the offices," Gupta said, rejecting media reports that they were chewing gums. He said he had also submitted a report to the FM containing 11 recommendations.

However, playing down the controversy on hiring of an outside agency for a sensitive office like the FM's, Gupta, who is also the joint MD of the private agency BCL Security, said: "My checks were in an individual capacity".