The National Cyber Security Centre has issued another wave of warnings towards government departments using Kaspersky anti-virus software.

Kaspersky labs has been accused of being used by Russian spies for espionage in the US, and now the UK's cybersecurity agency wants to warn British users. It believes the software could be exploited by the Russian Government.

Kaspersky Labs chief executive Eugene Kaspersky has outright denied the claims and believes the rumours were likely due to a co-ordinated campaign by US politicians, the FBI and media. About 400 million people use the anti-virus software worldwide.

The NCSC does not have any evidence of espionage taking place and is instead basing its precaution on risk-analysis, the BBC reports.

NCSC technical director Ian Levy said: "Given we assess the Russians do cyber-attacks against the UK for reasons of state, we believe some UK Government and critical national systems are at increased risk."

Ciaran Martin, head of the National Cyber Security Centre, says "Russia is acting against the UK's national interest in cyberspace."

In a letter dated 1 December to civil service chiefs, he said Russia seeks "to target UK central government and the UK's critical national infrastructure." He advised that "a Russia-based provider should never be used" for systems that deal with issues related to national security.

The agency says it's not advising the public at large against using Kaspersky's popular antivirus products.

On 28 November, the Russian CEO spoke out at Kaspersky Lab's London headquarters to a small pool of UK media, including IBTimes UK, giving a short presentation about what he believed could be behind suggestions his products could be used to spy on users.

"We never help the espionage agencies," he pledged. "It doesn't matter, the Russians or any other nation. It's the same as if the British government came to this office and asked us to do [something] wrong. If the Russian government comes to me and asks me [or my employees] to do anything wrong I will move the business out of Russia."

In mid-September, the US government banned federal agencies from using Kaspersky software amid concerns it could be used by the Kremlin to spy. Earlier this month, UK intelligence agency GCHQ told The Financial Times it was also worried about the anti-virus products.

Controversy was further fueled after it emerged the firm's consumer software had lifted secretive source code from a computer belonging to a National Security Agency (NSA) staffer who had taken hacking tools home, first reported by the Wall Street Journal in early October.

Kaspersky, who was trained as a mathematician in a KGB institute, said his company was under attack from nefarious forces - and noted it was because it was so good at its job.

The CEO also stressed that, globally, the overall company is continuing to grow.

"Why are we under attack? Because we are the best," Kaspersky explained. "We see malicious code to which others are blind.

"This is the only scenario because we didn't do anything wrong. We were just protecting our customers, visibly better than our colleagues."

He denied that the Kremlin had ever inserted itself into company affairs, instead indicating that he believed the sudden spike in attention arose as a result of a clandestine conspiracy.

"Yes, because it happened at the same time," he noted. "The FBI, the government and the media - coincidence? Its as much coincidence as my name in the company's name."

Kaspersky added: "There was something extraordinary. We did something that made someone very very very disappointed. The one thing which comes to mind is that we just do our job, we do our job much better than our competitors. I am not going to change our behaviour.

"These media attacks will never stop us."