2000 (earlier as the name of a software company), "software that automatically displays or downloads advertising," from ad (n.) + -ware, abstracted from software, etc.
Entries linking to adware
ad n.
abbreviation of advertisement, attested by 1841. Long resisted by those in the trade, and according to Mencken (1945) denounced by William C. D'Arcy (president of Associated Advertising Clubs of the World) as "the language of bootblacks, ... beneath the dignity of men of the advertising profession."
software n.
by 1851, soft-wares, "woolen or cotton fabrics," also, "relatively perishable consumer goods," from soft + ware (n.). The use in reference to computers is a separate coinage, attested by 1960, based on hardware in the computing sense.