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                                                                       Exhibit 5


                                    August 23, 2000


About.com, Inc.
220 East 42nd Street, 24th Floor
New York, New York 10017

            Re:   About.com, Inc. - Registration Statement on Form S-8
                  for Offering of an Aggregate of 115,808
                  Shares of Common Stock

Ladies and Gentlemen:

            We have acted as counsel to About.com, Inc., a Delaware corporation
(the "Company"), in connection with the registration on Form S-8 (the
"Registration Statement") under the Securities Act of 1933, as amended, of an
aggregate of 115,808 shares of the Company's common stock (the "Shares") and
related stock options authorized for issuance under the 1999 Stock Option Plan
of WiseAds Interactive, Inc. (the "Plan").

            This opinion is being furnished in accordance with the requirements
of Item 8 of Form S-8 and Item 601(b)(5)(i) of Regulation S-K.

            In our capacity as your counsel in connection with your preparation
and filing of the Registration Statement, we are familiar with the proceedings
taken and proposed to be taken by the Company in connection with the
authorization, issuance and sale of the Shares pursuant to the Plan, and for
purposes of this opinion, have assumed such proceedings will be timely completed
in the manner presently proposed. In addition, we have made such legal and
factual examinations and inquiries, including an examination of originals or
copies certified or otherwise identified to our satisfaction of such documents,
corporate records and instruments, as we have deemed necessary or appropriate
for purposes of this opinion. In our examination, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals and the conformity to authentic original documents of all documents
submitted to us as copies.

            We are opining herein as to the effect on the subject transaction
only of the internal laws of the State of New York and the General Corporation
Law of the State of Delaware, and we express no opinion with respect to the
applicability thereto, or the effect thereon, of the laws of any other
jurisdiction, or, in the case of Delaware, any other laws, or as to any matters
of municipal law or the laws of any local agency within any state.

            Subject to the foregoing, we are of the opinion that, if, as and
when the Shares have been issued and sold (and the consideration therefor
received) pursuant to the provisions of option agreements duly authorized under
the Plan, such Shares will be duly authorized, legally issued, fully paid and
nonassessable.
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                                                                 August 23, 2000
                                                                          Page 2


            We consent to the filing of this opinion letter as Exhibit 5 to the
Registration Statement.

            This opinion letter is rendered as of the date first written above
and we disclaim any obligation to advise you of facts, circumstances, events or
developments which hereafter may be brought to our attention and which may
alter, affect or modify the opinion expressed herein. Our opinion is expressly
limited to the matters set forth above and we render no opinion, whether by
implication or otherwise, as to any other matters relating to the Company, the
Plan or the Shares.

                                    Very truly yours,


                                    /s/ BROBECK, PHLEGER & HARRISON LLP
                                    ------------------------------------
                                    BROBECK, PHLEGER & HARRISON LLP