Making the electricity grid greener is boosting its vulnerability to computer hacking, increasing the risk that spies or criminals can cause blackouts.

Adding wind farms, solar panels and smart meters to the power distribution system opens additional portals through which hackers can attack the grid, according to computer security experts advising governments and utilities. Where traditionally the grid took power from a few sources, it’s now absorbing it from thousands.

The communication networks and software that link green energy sources to the grid as well as the electronic meters that send real time power usage to consumers and utilities are providing new back-door entry paths for computer hackers to raise havoc with the grid. The disclosure this week that hackers known as “Dragonfly” and “Energetic Bear” gained access to power networks across the U.S. and Europe in the past 15 months is a reminder of how vulnerable the system has become.