King said the objective of such an “unprecedented” cyber threat was to “interfere” in the democratic process and “manipulate public opinion”
His warning comes after Washington blamed Moscow for interfering in the US election.
Analysts say Russia's objective is to destabilise and highlight fault lines within the EU.
Washington accused Moscow of launching an unprecedented hacking campaign aimed at disrupting and discrediting the recent US election.
The US government formally blamed the Russian government for the hacks of Democratic Party emails and their subsequent disclosure via WikiLeaks and other entities. Russia has denied these accusations.
Addressing a cyber conference in Brussels, King said, “As our dependence on the internet increases so does our vulnerability.
“We in Europe currently face an unprecedented level of cyber threat from hostile actors,” said King. “And the biggest threat right now is in the form of cyber espionage from hostile states.
“This is something we saw in the recent US elections. It is designed to destabilise and/or undermine and influence elections in the west.”
Russia was widely seen as being behind the hacks of Democratic Party emails and, without mentioning Russia, King said it appeared that such attacks were linked to “groups very close to state authorities.”
King, appointed earlier this year, said, “There is form, let’s remember, because there have been similar attacks against TV stations, political parties and the EU institutions, including most recently a cyber attack against the European Parliament’s IT systems earlier this year.”
He warned that malicious attacks and cyber incidents are growing in sophistication and threaten the information technology systems that underpin the vast majority of the critical and non-critical infrastructure in Europe.
“These types of hostile, state-connected interventions are something we in Europe need to be aware of because, with upcoming national elections in France and Germany in 2017, this is a problem that is likely to increase.
“It is happening all the time but especially during electoral cycles and it is likely that cyber attacks will be used to try and influence these very important elections next year in Europe.”
King, who opened the day-long conference on 17 November, pointed out that the Commission had taken action to combat such a threat, citing the existence of the European Cyber Crime Centre and Eurojust.
King said the goal of such initiatives is to create a “secure” digital environment where all economic actors and citizens can safely take advantage of the benefits offered by digital in Europe.
King was a keynote speaker at the fourth annual European Cyber Security Conference, organised by Forum Europe.
He added, “We must strengthen our resilience to this sort of threat, including increasing cooperation between member states and all those involved. We must make the EU and Europe a less attractive target for cyber attacks.”
He added, “Creating effective cyber attack mechanisms will be a challenge and no single member state, or sector, can do it alone.”
His comments are echoed by US President Barack Obama who, speaking at a news conference in Peru on Friday, said it was clear more work remained to protect the US from cyber attacks against US infrastructure, financial systems, and government.
“Both state and non-state actors are getting better and better at it, and it is becoming more rapid,” Obama said. “It is inevitable that we will have to modernise and update not only the tools we use to defend those assets and the American people, but also how we organise it.”
Elsewhere, German Chancellor Angela Merkel told a weekend conference that Germany already faced "a daily task" of responding to Russian cyber attacks and a disinformation campaign.
"We are already, even now, having to deal with information out of Russia or with internet attacks that are of Russian origin or with news which sows false information."
Analysts say that Russia targets Germany with cyber attacks and disinformation in an attempt to deepen existing divisions within Europe's largest economy and destabilise the EU.
Germany has sided with the United States and been at the centre of the EU's response to Russia's annexation of Crimea and support for rebels in eastern Ukraine. Russia, it is claimed, is seeking to sow divisions within the EU and Germany in order to unwind EU-imposed sanctions.