Senior Congress leader P Chidambaram on Wednesday said the solicitor general telling the Supreme Court that the government has information which he cannot divulge in public by way of an affidavit is a "confession" that software-spyware was used, and sought to know if it was Pegasus and for what purpose it was used.

The Centre on Tuesday told the Supreme Court that divulging information on whether the country uses spyware like Pegasus or not would involve national security aspect as enemies of the nation or those indulging in terror activities would change or modulate their software.

Reacting to the development, Chidambaram said, "SG tells SC that the government has information which he cannot divulge in public by way of affidavit. That is a confession that software-spyware was used. For what, we do not know."

"We want to know if that spyware-software was called Pegasus and for what purpose was it used," the former home minister said in a series of tweets.

"If the government answers these two questions, the remaining questions will answer themselves in due course," Chidambaram said.

On Tuesday night, Chidambaram had tweeted that the Israel-based NSO Group has admitted and said that Pegasus is spyware and is used to hack phones.

"Why is the government reluctant to answer the question, 'Did any of the agencies buy Pegasus spyware and use it?' We want a straight answer," he had said.

"If it has not come today, it will certainly come on a future day. The Supreme Court must demand an answer to the question. I hope the Court will," Chidambaram had tweeted on Tuesday.

Solicitor General Tushar Mehta, appearing for the Centre, told a bench headed by Chief Justice N V Ramana that those involved in terror activities may take pre-emptive steps if the government divulges details of which software is used for various purposes including interception.

The apex court, which made clear that it did not want the government to disclose anything which compromises national security, issued notice to the Centre on the batch of pleas seeking an independent probe into the alleged Pegasus snooping matter and posted the matter for hearing after 10 days.

During the arguments, Mehta said this cannot be a subject matter of affidavit and public debate and the government has said in its limited affidavit that it will constitute a committee of experts to examine all the aspects of the Pegasus issue.