NEW YORK (AP) — Activist investment firm Starboard Value says it bought an 8.2 percent stake in armored car company Brink's, and it called the stock undervalued.

Starboard Value disclosed ownership of almost 4 million shares in a form filed with the Securities and Exchange Commission on Monday. According to FactSet, that would make Starboard the second-largest owner of Brink's shares.

Starboard Value LP started buying shares of the Richmond, Virginia-based company March 10. It didn't disclose any specific problems with Brink's or its management, but said the shares were undervalued and an attractive investment opportunity.

Starboard Value has pushed Internet giant Yahoo to make big changes, including spinning off some businesses, and in 2014 it took control of Darden Restaurants Inc., the owner of the Olive Garden chain, after criticizing Darden's previous leadership.

Brink's Co. began climbing in February after Brink's reported its fourth-quarter results and rose further after the company's first-quarter report on Friday. The shares are up 25 percent in 2015 and closed at $30.61 on Monday.

The shares rose 74 cents, or 2.4 percent, to $31.35 in aftermarket trading.

Brink's took a loss in 2014 as its business was hurt by factors including the strong U.S. dollar and currency devaluation in Venezuela. Its annual revenue fell 6 percent to $3.56 billion. On Friday the company lowered its revenue outlook but maintained its profit estimate. Brink's said its U.S. and Mexico businesses did well and said it was able to cut corporate spending.

The company is currently forecasting adjusted net income of $1.55 to $1.75 per share on $3.1 billion in revenue.