BOSTON (Bloomberg) — Tyco International, the world's biggest maker of security systems through its ADT unit, agreed with a lender to extend the maturity of a $500 million bridge loan by six months.

The date was pushed to June 15 from December 15, Bermuda-based Tyco said in a US Securities and Exchange Commission filing.

Citibank N.A. is the administrative agent and a lender on the agreement.

Tyco spun off health-care company Covidien and electrical components-maker Tyco Electronics on June 29 in an effort to increase returns to shareholders. The company raised its quarterly dividend 36 percent last month and authorised a $1 billion share buyback programme.