BOSTON (Reuters) - Bermuda-based Tyco International Ltd.'s ADT security alarm business is under fire on four continents as the unit's accounting problems and contract disputes threaten to undermine the conglomerate's efforts to regain credibility.

Less than a week after firing the head of its fire and security division, Tyco yesterday said two executives in that division face criminal charges in Mexico after a judge issued a warrant for their arrest, alleging fraud over ADT alarm contracts.

ADT's decentralised operations pose a significant threat to Tyco because they escaped close scrutiny under former senior management, Tyco executives said last week.

Tyco downplayed the arrest warrants for Phil McVey, vice president of fire and security's Latin American operations, and Patricio Gonzalez, technical director for ADT in Mexico.

"We have confidence that in the end, this dispute will be resolved in favour of our employees," Tyco said in a statement. "We are pursuing all possible options to protect our employees and resolve this matter as fairly as possible.

Tyco said former ADT dealers "abused the Mexican justice system" to turn civil claims into a criminal case.

Claims against ADT are not isolated to Mexico, though. In Australia, alarm firms are seeking court claims against ADT, alleging ADT changed contracts without approval and removed funds earmarked for marketing and development.

Tyco has made a number of changes to a program that pays independent security companies to land customers and install alarm equipment for ADT. These actions have rankled current and former ADT independent dealers throughout the world.

Tyco has conceded ADT operations have booked revenue prematurely, failed to write off equipment on disconnected accounts and signed up customers with low credit scores.

Persistent accounting worries and criminal charges against former senior executives have battered Tyco's image and stock over the past year.

Tyco shares, which were up 17 cents to $12.63 in late Tuesday trade on the New York Stock Exchange, are off nearly 26 percent this year as investors learn the company's problems extend beyond the home office. ADT-related controversy has surfaced in North America, Asia, Europe and Australia over the past several months as Tyco scrambles to review its accounting and business practices.

ADT is a key part of Tyco Fire & Security, an operation expected to generate about $11 billion in revenue this year.