One in five women admit to logging on to their partner's email or social network surreptitiously, according to research from security company Norton. One in 10 men admitted to doing likewise.
The research reveals a growing trend of cyber snooping in the UK.
Thirteen per cent of Brits also admitted to having lied about their age online or to having adopted a fake identity.
The report also found that 19 Brits fall victim to an online crime a minute. However, only 16 per cent of cyber crimes are being reported to police.
The survey, which was conducted by StrategyOne, polling 20,000 people across 24 countries, found three times as many people in the UK had fallen victim to online crime than had suffered from street crime in the last twelve months. Norton estimates that online crime cost Brits around £1.1 billion a year.
Yet it isn't all bad news, with more than half (52 per cent) of under 25-year-olds saying they shared the email or social network password with their partner. For the 45-54 age group, that figure dropped to 33 per cent.
"Cybercrime is hitting Brits in the pocket," said Sam Ellis, a security expert at Norton. "But the report also found questionable online ethics among the general population."
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