Oil and gas companies are facing increasingly sophisticated hackers seeking to steal trade secrets and disrupt operations, according to a newspaper investigation.

A stretch of the Gulf Coast near Houston features one of the largest concentrations of refineries, pipelines, and chemical plants in the country, and cybersecurity experts say the region is a target for espionage and other cyberattacks.

The Houston Ship Channel is a hub for energy facilities.Homeland Security, which is responsible for protecting the nation from cyber crime, received reports of some 350 incidents at energy companies from 2011 to 2015, an investigation by the Houston Chronicle has found. Over that period, the agency found nearly 900 security flaws within U.S. energy companies, more than any other industry.

Steps are being taken to thwart attacks. For instance, the Coast Guard in a joint operation with Houston police patrolled the waters southeast of Houston last year conducting sweeps for unprotected wireless signals that hackers could use to gain access to facilities. The operation was one of the first of its kind in the U.S. concentrating on cyberattacks by sea.

But the network of oil and gas operations makes it difficult to secure. Thousands of interconnected sensors and controls that run oil and gas facilities remain rife with weak spots.

Many companies lack the technology and personnel to detect hackers. Equipment was designed decades ago without security features, and efforts over the years to link computer networks to devices that monitor pressure or control valves have exposed operations to online threats.

Power, chemical and nuclear facilities must adhere to cybersecurity measures, but federal law doesn't impose such standards on the oil and gas sector. And when oil and gas companies have been infiltrated by a hacker, they are not required to report the incident, the news report says.