OLSHAN GRUNDMAN FROME ROSENZWEIG & WOLOSKY LLP

                                  [LETTERHEAD]


                                                              June 25, 2001


Network-1 Security Solutions, Inc.
1601 Trapelo Road, Reservoir Place
Waltham, Massachusetts  02451

     Re:  Registration Statement on Form S-8
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Ladies and Gentlemen:

     We have acted as counsel for Network-1 Security Solutions, Inc., a Delaware
corporation (the "Company"), in connection with the preparation and filing of a
Registration Statement on Form S-8 (the "Registration Statement") with the
Securities and Exchange Commission (the "Commission"), with respect to the
registration under the Securities Act of 1933, as amended (the "Act"), of an
aggregate of 735,000 shares (the "Shares") of common stock, par value $.01 per
share (the "Common Stock"), to be issued pursuant to the Company's Amended and
Restated 1996 Stock Option Plan (the "Plan").

     In connection with the registration of the Shares, we have reviewed copies
of the Registration Statement, the Plan, the Company's Certificate of
Incorporation, as amended, the Company's Bylaws, and such documents and records
as we have deemed necessary to enable us to express an opinion on the matters
covered hereby.

     We have also examined and relied upon representations, statements or
certificates of public officials and officers and representatives of the
Company.

     In all such examinations, we have assumed the completeness and authenticity
of all records and documents submitted to us as originals and the conformity to
original records and documents of all copies submitted to us as reproduced or
conformed copies.
OLSHAN GRUNDMAN FROME ROSENZWEIG & WOLOSKY LLP

Network-1 Security Solutions, Inc.
June 25, 2001
Page 2 of 2 pages






     Based upon the foregoing, we are of the opinion that the Shares covered by
the Registration Statement, upon the granting of the options described in the
Plan and upon delivery of such Shares and payment therefor at the prices and in
accordance with the terms stated in the Plan, will be validly issued, fully paid
and non-assessable.

     A member of this firm holds options to purchase an aggregate of 14,828
Shares.

     We hereby consent to the filing of this opinion letter as an exhibit to the
Registration Statement. In giving such consent, we do not thereby admit that we
are within the category of persons whose consent is required under Section 7 of
the Act or the rules and regulations of the Commission thereunder.

     We are delivering this opinion to the Company, and no person other than the
Company may rely on it.

                              Very truly yours,

                              /s/ OLSHAN GRUNDMAN FROME ROSENZWEIG & WOLOSKY LLP
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                              OLSHAN GRUNDMAN FROME ROSENZWEIG & WOLOSKY LLP