Many internet users routinely check what their spouse is doing online
A fifth of married internet users regularly snoop on their spouses' emails and text messages, Oxford University researchers say.
The survey found general agreement between couples about the acceptability of certain online behaviours.
But 46% of the 2,401 married people asked by the Oxford Internet Institute disagreed on whether it was acceptable for partner to visit adult sites.
Men were more likely to accept such behaviour in their partner than women.
Meanwhile, 13% of respondents admitted to checking up on their partner's browser history.
Unsurprisingly, 97% would be unhappy about their partner falling in love with someone else via the internet.
Other extra-marital online activities considered beyond the pale include: cyber-sex (94%), disclosing intimate details (92%), communicating relationship troubles (89%), sharing personal information about a partner (88%), and flirting (85%).
The researchers also found that just 6% of married internet users first encountered their partner online - with 34% of those finding true love on a dating site.
Of those who met in the real world, pubs (25%), work (19%) and friends (14%) were the most popular ways to find a soul mate.
Couples that met online were most likely to have different levels of education (36% compared with 21% of "offline" couples) and an age gap of more than six years (39% compared with 24%).
Just 10% considered the internet important in maintaining their relationship - with most opting to keep the flame alight by the tried and tested method of face-to-face communication.
The survey was conducted by ICM Research and consisted of 2,401 married internet users in the UK.