The European Union leads the world in the number of computers that are controlled remotely by hackers.
Data from email security specialist CipherTrust shows that 26 per cent of all PCs infected in May are located in the EU, compared with 20 per cent in the US and 15 per cent in China.
To help track the activity of zombie systems CipherTrust has built an interactive map detailing the number of systems controlled by hackers around the world.
"The launch of our ZombieMeter furthers our commitment to making this information available to the email community," said Dr Paul Judge, chief technology officer at CipherTrust.
"Over the past year, our researchers have continued to analyse the information to identify threats such as zombie activity, virus patterns and phishing attacks.
"By monitoring global messaging activity and identifying behavioural patterns, we can continue to provide predictive protection against the threats before they emerge."
The UK accounted for three per cent of the world's total, with Germany leading Europe at six per cent. Over May an average of 172,000 new PCs were infected each month.
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