$4 billion takeover by Republic Industries Ltd., raised its stake in the security company on the day the deal was called off.

According to Securities and Exchange Commission filings, Western bought 1.3 million ADT common shares on September 30 at $18.25 to $19 a share. The purchases raised Western's stake to 24.1 percent from 23.2 percent.

Investment analyst Mark Baylin with Baltimore-based T. Rowe Price Associates said Western's move was consistent with previous acquisitions of ADT stock.

"One of the explanations is that they have an interest at some point in owning the company,'' he said.

Western Resources opposed the Republic Industries bid to acquire ADT, a Bermuda-registered company that operates a security business and a used-car auction house. Western Resources has its own security business.

Western may also be protecting itself against future takeover bids, Mr. Baylin said.

ADT shares traded as low as $18 on September 30, the day that Republic scuttled its bid, and closed at $19.

Republic provides waste and electronic security services. Its largest shareholder is Bermuda resident Michael DeGroote.