EXHIBIT 5.1
                                                                     -----------




                                                              September 27, 2005


Securities and Exchange Commission
450 Fifth Street, N.W.
Judiciary Plaza
Washington, D.C.  20549


Re:      Network-1 Security Solutions, Inc.
         Amendment No. 1 on Form S-2 to Form S-3
         Registration Statement File No. 333-126013
         ------------------------------------------

Gentleman:

         Reference is made to Amendment No. 1 on Form S-2 to Form S-3
Registration Statement dated September 27, 2005 (the "Registration Statement"),
filed with the Securities and Exchange Commission by Network-1 Security
Solutions, Inc., a Delaware corporation (the "Company"). The Registration
Statement relates to the resale of an aggregate of 16,886,267 shares (the
"Shares") of the Company's Common Stock, $.01 par value (the "Common Stock") of
which an aggregate of 5,729,588 Shares are issuable upon the exercise of certain
warrants and options issued by the Company.

         We advise you that we have examined original or copies certified or
otherwise identified to our satisfaction of the Certificate of Incorporation and
By-laws of the Company, minutes of meetings of the Board of Directors and
stockholders of the Company, the Registration Statement, and such other
documents, instruments and certificates of officers and representatives of the
Company and public officials, and we have made such examination of the law as we
have deemed appropriate as the basis for the opinion hereinafter expressed. In
making such examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as certified or photostatic
copies.
September 26, 2005
Page 2





         Based upon the foregoing, we are of the opinion that:

         The 16,886,267 Shares including an aggregate of 5,729,588 Shares
issuable upon the exercise of certain outstanding warrants and options, have
been duly authorized and reserved for and when issued in accordance with the
terms of each respective security will be legally issued, fully paid and
non-assessable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and we further consent to the reference to this firm
under the caption "Legal Matters" in the Registration Statement and the
Prospectus forming a part thereof.





                                Very truly yours,

                                /s/ EISEMAN LEVINE LEHRHAUPT & KAKOYIANNIS, P.C.

                                EISEMAN LEVINE LEHRHAUPT & KAKOYIANNIS, P.C.