The 49ers announced the moves Thursday.
San Francisco signed Brock as an undrafted rookie out of Minnesota in 2010. He earned a spot on the opening day roster that year, had two interceptions in 11 games in 2011 and tied for the special teams lead with 15 tackles last season.
Hastings joined the 49ers as an undrafted rookie in 2011, when he spent most of the season on the practice squad. He made his NFL debut on New Year's Eve that year at St. Louis. He was released during training camp last season and will again be a long shot to make the team.
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