The life of a trucker was once a solitary one, with an open road and little more than a radio to connect to the wider world. Now, vehicles are packed with technology, opening the door to hackers, experts warn.

Most commercial trucks at major operators are now equipped with GPS systems that relay information—such as route and speed—to a central hub. Other technologies can collect information to gauge whether a driver is falling asleep.

The industry’s growing reliance on technology means that bad actors could divert valuable cargo from its destination, paralyze logistical networks or enable trade secrets to be compromised, according to some in the industry. Hackers are already making attempts to break in.

“From a private-industry standpoint, we are facing this huge hockey stick of [attempted] attacks,” said Sharon Reynolds , chief information security officer at Dallas-based fleet-management technology provider Omnitracs LLC and the president of the North Texas chapter of InfraGard, a security partnership between businesses and the Federal Bureau of Investigation.

Trucking accounted for 71% of domestic freight shipments by value in 2017, according to the Transportation Department. This means that even small disruptions can have major consequences, said Gil Hecht , chief executive and founder of security firm Continuity Software Ltd.

“The main implication of all of these technology trends is that the transportation industry, which was considered a ‘slow’ industry in the past, is becoming a ‘fast’ industry, one which is much more sensitive to being 24/7 available,” he said.

Ground freight is a valuable target on a number of fronts, according to Michael Overly, a partner at law firm Foley & Lardner LLP. While cargo has an intrinsic value, the data on what is being transported, and where, can also be a prized asset for the right people.

The data could be useful for corporate espionage and other criminal purposes, he said: “If we know for example that large companies started to ship certain types of materials to certain locations, we might be able to reach conclusions as to what might be done at that location or what might be done in the future at that location.”

Attackers have more ways than ever of getting into vehicles’ digital guts. Most trucks carry onboard systems, for instance, that will require a mechanic at a maintenance stop to connect a computer to diagnose mechanical problems accurately. Even basic technologies are providing connections between vehicles.

Concerns about cybersecurity in trucking have also been fueled by the mandate for electronic logging devices, or ELDs, on most trucks, effective since December 2017. The rule is designed to improve safety by replacing easily doctored paper logging systems for hours worked and distance traveled, among other metrics.

Critics say that a lack of uniform standards around the new devices has increased cybersecurity risks for drivers. Michael Phillips , head of cyber, media and technology claims for insurer Allianz SE’s corporate and specialty business in North America, said that not all ELDs “are created equal,” and some might lack basic security measures such as encryption.

“The ELD cyber risk is a triple threat. A vulnerable ELD might expose private data, reveal commercially sensitive information, or disrupt a trucking firm’s business,” he said.

Ultimately, trucking and ground freight, like similar critical infrastructure sectors such as maritime shipping, is an industry made up of participants of different sizes and levels of sophistication.

With the introduction of connected technology comes some cybersecurity risk, no matter how well designed the technology might be, said Stephen Viña , a senior vice president in the cyber practice at Marsh & McLennan Cos.’ Marsh business.

“A lot of companies, not just in the transportation sector, are trying to keep up with the risks that are being introduced to their business by new technologies,” he said.

Write to James Rundle at james.rundle@wsj.com