NetScout Systems (NTCT) 10-K 2003 FY Annual report

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99.1

CERTIFICATION PURSUANT TO SECTION 906 OF
THE SARBANES-OXLEY ACT OF 2002

        In connection with the Annual Report of NetScout Systems, Inc. (the "Company") on Form 10-K for the period ended March 31, 2003, as filed with the Securities and Exchange Commission on the date hereof (the "Report"), I, Anil K. Singhal, Chief Executive Officer of the Company, hereby certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that: (1) the Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and (2) the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/  ANIL K. SINGHAL      Anil K. Singhal
Chief Executive Officer

June 12, 2003

A signed original of this written statement required by Section 906 has been provided to the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.

QuickLinks

CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002