The 49ers on Thursday signed an undrafted rookie defensive back and waived a standout defensive lineman from the now-defunct Alliance of American Football.

The 49ers announced the signing of cornerback Alex Brown to a three-year contract. Brown, an undrafted rookie from South Carolina State, attended the team’s rookie minicamp two weeks ago.

The 49ers waived defensive lineman Damontre Moore to make room for Brown on the 90-man roster. Moore played for the San Diego Fleet of the AAF. He recorded 22 tackles, seven sacks and a fumble recovery this spring in the short-lived professional league.

[RELATED: Jason Verrett nearly retired after tearing Achilles]

Brown (5-foot-11, 170 pounds) was a second-team All-Mid-Eastern Athletic Conference selection as a senior. He appeared in 31 games with 25 starts during his career. He recorded 90 tackles, 26 passes defensed, seven interceptions and one sack.