The war in Ukraine has come with an ever-present threat of cyber catastrophe, as experts and US military officials remain on high alert for potential hacks. And while the big one has yet to come, the battle online continues to escalate.

UK intelligence officers warned on Thursday that Russia is increasingly seeking out cyber targets as its ground military campaign in Ukraine stalls. Additional reports on Wednesday revealed Russian hackers recently attempted to penetrate the networks of Nato and the militaries of some eastern European countries.

These developments showed that “things are heating up” on the cyber front, said Theresa Payton, cybersecurity expert and former White House chief information officer. “We should prepare for the worst and operate at our best,” she said.

Still, Payton noted, Russia had been very slow to deploy cyber tactics in the war to date. There could be a number of reasons for this, she said: Putin might not feel the need to use cyber-attacks in his strategy at this juncture in the war, or he might want to avoid additional retaliation promised by the US in the case of a cyberwar.

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Putin might also be “playing a long game” and having his cyber operatives infiltrate various adversaries and gain footholds, then wait until he decides to launch a cyber-attack.

“It is possible that digital attacks are under way and not fully understood in the fog of a ground war,” Payton said.

Although Russia has been slow to carry out major attacks, it has been targeting Ukraine in other ways. On 24 February, more than 10,000 modems of the satellite broadband provider Viasat were knocked offline in a hack that US officials have attributed to Russia.

Although that attack sabotaged hardware across Ukraine and is continuing, it was more likely Russia would focus its resources on cyber reconnaissance missions than forceful attacks, said Glenn S Gerstell, former general counsel of the National Security Agency and Central Security Service.

“We know Russia is quite sophisticated in cyber surveillance and in spying on their adversaries, and we can assume they would want to find out about sanctions and other intel,” he said.

The US announced additional sanctions against Russia, including on its technology sector, this week. The White House said on Thursday that the US had evidence that the war against Ukraine had been “a strategic disaster” for Russia and would only worsen as sanctions increased.

Gerstell said it was difficult to foresee what kind of offensive Russia would launch because its strategy throughout this conflict had been unpredictable. But Putin’s response might change as the situation on the ground does, he added.

“As they begin to lose, Putin may stray from what we think of as rational calculations of risk and reward,” Gerstell said. “If his rule is threatened, all bets are off on what thresholds he may cross in terms of cyber response.”

Reuters contributed to this report