NETWORK-1 SECURITY SOLUTIONS, INC.


                        Filed Pursuant to Rule 424(b)(3)
                           Registration No. 333-126013

                           PROSPECTUS SUPPLEMENT NO. 5
                     (To Prospectus dated December 22, 2005)


This is a prospectus supplement to our prospectus dated December 22, 2005 (the
"Prospectus") relating to the resale from time to time by selling stockholders
of up to 16,886,267 shares of our Common Stock, including shares issuable upon
exercise of outstanding warrants and options. On March 31, 2006, we filed with
the Securities and Exchange Commission a Form 12b-25. The text of the Form
12b-25 is attached to and a part of this supplement.

This prospectus supplement should be read in conjunction with the Prospectus and
the prior prospectus supplements, and may not be delivered or utilized without
the Prospectus and the prior prospectus supplements. This prospectus supplement
is qualified by reference to the Prospectus, except to the extent that the
information provided by this prospectus supplement supersedes the information
contained in the Prospectus.

The securities offered by the Prospectus involve a high degree of risk. You
should carefully consider the "Risk Factors" referenced on page 7 of the
Prospectus in determining whether to purchase the Common Stock.

The date of this prospectus supplement is March 31, 2006.


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                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                   FORM 12b-25

                                               Commission File Number 1-14896

                           NOTIFICATION OF LATE FILING

(Check One):   [X] Form 10-K    [_] Form 11-K    [_] Form 20-F    [_] Form 10-Q
               [_] Form N-SAR

          For Period Ended: December 31, 2005

          [_]  Transition Report on Form 10-K
          [_]  Transition Report on Form 20-F
          [_]  Transition Report on Form 11-K
          [_]  Transition Report on Form 10-Q
          [_]  Transition Report on Form N-SAR

          For the Transition Period Ended:______________________________________

     Read attached instruction sheet before preparing form. Please print or
type.

     Nothing in this form shall be construed to imply that the Commission has
verified any information contained herein.

     If the notification relates to a portion of the filing checked above,
identify the item(s) to which the notification relates: ________________________




                                     PART I
                             REGISTRANT INFORMATION

Full name of registrant      NETWORK-1 SECURITY SOLUTIONS, INC.

Former name if applicable

________________________________________________________________________________

Address of principal executive office (Street and number)

445 Park Avenue, Suite 1028
________________________________________________________________________________

City, state and zip code

New York, New York  10022
________________________________________________________________________________



                                    PART II
                             RULE 12b-25(b) AND (c)

     If the subject report could not be filed without unreasonable effort or
expense and the registrant seeks relief pursuant to Rule 12b-25(b), the
following should be completed. (Check box if appropriate.)

     [X]   (a)  The reasons described in reasonable detail in Part III of this
                form could not be eliminated without unreasonable effort or
                expense;
     [X]   (b)  The subject annual report, semi-annual report, transition report
                on Form 10-K, 20-F, 11-K or Form N-SAR, or portion thereof will
                be filed on or before the 15th calendar day following the
                prescribed due date; or the subject quarterly report or
                transition report on Form 10-Q, or portion thereof will be filed
                on or before the fifth calendar day following the prescribed due
                date; and
     [_]   (c)  The accountant's statement or other exhibit required by Rule
                12b-25(c) has been attached if applicable.



                                    PART III
                                    NARRATIVE

     State below in reasonable detail why the Form 10-K, 11-K, 20-F 10-Q, N-SAR
or the transition report portion thereof could not be filed within the
prescribed time period. (Attach extra sheets if needed.)

     The Company is unable to file its Form 10-KSB for the year ended December
31, 2005 at this time because of certain issues pertaining to the Company's
financial statements which cannot be resolved without unreasonable effort or
expense.



                                    PART IV
                               OTHER INFORMATION

(1)  Name and telephone number of person to contact in regard to this
     notification

     Corey M. Horowitz, Chairman & CEO               (212)        829-5700
     ---------------------------------------------------------------------------
                       (Name)                     (Area Code) (Telephone Number)

(2)  Have all other periodic reports required under Section 13 or 15(d) of the
     Securities Exchange Act of 1934 or Section 30 of the Investment Company Act
     of 1940 during the preceding 12 months or for such shorter period that the
     registrant was required to file such report(s) been filed? If the answer is
     no, identify report(s).
                                                                 [X] Yes  [_] No

(3)  Is it anticipated that any significant change in results of operations from
     the corresponding period for the last fiscal year will be reflected by the
     earnings statements to be included in the subject report or portion
     thereof?
                                                                 [X] Yes  [_] No

     If so: attach an explanation of the anticipated change, both narratively
and quantitatively, and, if appropriate, state the reasons why a reasonable
estimate of the results cannot be made.

                       NETWORK-1 SECURITY SOLUTIONS, INC.
--------------------------------------------------------------------------------
                  (Name of Registrant as Specified in Charter)

Has  caused  this  notification  to be signed on its  behalf by the  undersigned
thereunto duly authorized.


Date: March 31, 2006           By /s/ David C. Kahn
      --------------              ---------------------------------------------
                                  Name:  David C. Kahn
                                  Title: Chief Financial Officer



     INSTRUCTION: The form may be signed by an executive officer of the
registrant or by any other duly authorized representative. The name and title of
the person signing the form shall be typed or printed beneath the signature. If
the statement is signed on behalf of the registrant by an authorized
representative (other than an executive officer), evidence of the
representative's authority to sign on behalf of the registrant shall be filed
with the form.





                                   ATTACHMENT

Form 12b-25/Network-1 Security Solutions, Inc.

(3) The Company anticipates that it will incur a net loss of approximately
$1,332,000 for the year ended December 31, 2005 as compared to a net loss of
$1,953,000 for the year ended December 31, 2004.