The recent hack on the Office of Personnel Management might not be the biggest cyber security issue the U.S. government needs to be worried about.

America's power grid, including water systems and other critical infrastructures, is full of vulnerable computer systems that, according to a Congressional Research Service (CRS) report that was made public this month, have been subject to an "increasing" amount of cyber attacks.

"In recent years, new threats have materialized as new vulnerabilities have come to light, and a number of major concerns have emerged about the resilience and security of the nation's electric power system," the report says. "In particular, the cyber security of the electricity grid has been a focus of recent efforts to protect the integrity of the electric power system.

"Although malware intrusions may not have resulted in a significant disruption of grid operations so far, they still have been possible even with mandatory standards in place."

The particular types of computer viruses in question "comb internal systems for private information in a clandestine manner," according to The Washington Free Beacon.

"Incidents of reported cyber intrusions and attacks aimed at undermining the U.S. grid appear to be increasing," according to the report. "Further, the electric grid is not isolated from attacks on other critical infrastructure sectors on which it depends (i.e., the natural gas subsector, water, and transportation), and mandatory and enforceable cyber security standards apply to only a few of the critical infrastructure sectors."

The issue is so serious that the report states there should be a fair amount of planning towards how to recover from a crippling attack, not just how to prevent one.

"Given the potential for damage to the nation's economy from a major cyberattack on the grid, some might suggest a greater focus on recovery is needed and should become as much a part of a cybersecurity strategy as are efforts to secure the system."