<PAGE>

                               HALE AND DORR LLP
                              Counsellors At Law
                 60 State Street, Boston, Massachusetts  02109
                        617-526-6000 * FAX 617-526-5000


                                    December 20, 1999


Engage Technologies, Inc.
100 Brickstone Square
Andover, MA 01810

     Re:  1999 Stock Option Plan for Non-Employee Directors
          -------------------------------------------------

Ladies and Gentlemen:

     We have assisted in the preparation of a Registration Statement on Form S-8
(the "Registration Statement") to be filed with the Securities and Exchange
Commission under the Securities Act of 1933, as amended (the "Securities Act"),
relating to an aggregate of 250,000 shares of Common Stock, $.01 par value per
share (the "Shares"), of Engage Technologies, Inc., a Delaware corporation (the
"Company"), issuable under the Company's 1999 Stock Option Plan for Non-Employee
Directors (the "Plan").

     We have examined the Certificate of Incorporation and By-Laws of the
Company, each as amended and restated to date and originals, or copies certified
to our satisfaction, of all pertinent records of the meetings of the directors
and stockholders of the Company, the Registration Statement and such other
documents relating to the Company as we have deemed material for the purposes of
this opinion.

     In our examination of the foregoing documents, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to original documents of all documents submitted to
us as copies, the authenticity of the originals of such latter documents and the
legal competence of all signatories to such documents.

     We assume that the appropriate action will be taken, prior to the offer and
sale of the Shares in accordance with the Plan, to register and qualify the
Shares for sale under all applicable state securities or "blue sky" laws.

     We express no opinion herein as to the laws of any state or jurisdiction
other than the state laws of The Commonwealth of Massachusetts, the Delaware
General Corporation Law statute and the federal laws of the United States of
America.
<PAGE>

     Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized for issuance and, when the Shares are issued
and paid for in accordance with the terms and conditions of the Plan, the Shares
will be validly issued, fully paid and nonassessable.

     It is understood that this opinion is to be used only in connection with
the offer and sale of the Shares while the Registration Statement is in effect.

     Please note that we are opining only as to the matters expressly set forth
herein, and no opinion should be inferred as to any other matters.

     We hereby consent to the filing of this opinion with the Commission as an
exhibit to the Registration Statement in accordance with the requirements of
Item 601(b)(5) of Regulation S-K under the Securities Act.  In giving such
consent, we do not hereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission.


                                    Very truly yours,


                                    /s/ Hale and Dorr LLP

                                    HALE AND DORR LLP