Spain's defence minister Margarita Robles warned on Friday of a possible cyberattack during the NATO summit in Madrid next week.
Asked if Spain feared Russia could launch such an attack, Robles told journalists "the possibility of a cyberattack exists", without mentioning the country by name.
"There are many challenges and many threats," she said, adding that there were "many people working... to prevent any situation that could affect security" at the summit on June 28-30.
According to the Barcelona daily La Vanguardia, Spanish intelligence services fear a Russian attack on strategic infrastructure such as airports, hospitals, or water and energy supply centres.
The Spanish capital will be under tight security.
Some 10,000 law enforcement officers have been deployed for the summit, which will be attended by US President Joe Biden, his French counterpart Emmanuel Macron, British Prime Minister Boris Johnson and German Chancellor Olaf Scholz.
Russia's invasion of Ukraine is set to dominate talks.
Recently, Microsoft accused state-backed Russian hackers to have been engaged in “strategic espionage” against governments, think tanks, businesses and aid groups in 42 countries supporting Kyiv.
“Since the start of the war, the Russian targeting (of Ukraine's allies) has been successful 29 percent of the time,” Microsoft President Brad Smith wrote, with data stolen in at least one-quarter of the successful network intrusions.
“As a coalition of countries has come together to defend Ukraine, Russian intelligence agencies have stepped up network penetration and espionage activities targeting allied governments outside Ukraine,” Smith said.
Nearly two-thirds of the cyberespionage targets involved NATO members. The United States was the prime target and Poland, the main conduit for military assistance flowing to Ukraine, was the second. In the past two months, Denmark, Norway, Finland, Sweden and Turkey have seen stepped-up targeting.
Affiliate links may be automatically generated - see our ethics statement for details.