The Chicago Fire Department has begun a previously planned $10 million upgrade of its emergency communications radio network from analog to digital technologies, the Chicago Tribune reported today.

The CFD has been plagued by several incidents involving racial slurs broadcast over its network over the past two months. The latest incident targeted recently appointed Commissioner Cortez Trotter, the city’s first African-American fire commissioner.

However, the CFD has steadfastly maintained that most of the incidents are the result of hackers who have taken over department frequencies to make the transmissions. Larry Langford, a CFD spokesman, told the Tribune the department is “99 percent sure” that the latest transmissions are the work of someone outside the department. The CFD has nearly completed the reprogramming of 1000 department radios to make them more hacker-resistant.

Digital systems are thought to be more difficult to hack into, because the radios are expensive and require “extensive software programming,” the Tribune said. In contrast, analog radios are inexpensive and easy to modify, enabling hackers to latch onto public-safety frequencies, the paper said.