Many people have come across others who they suspect are cheaters.
But the secrecy surrounding infidelity makes it difficult to gather much evidence.
Forbes magazine has done exactly that - compiling a list ranking the world's most unfaithful places.
It analysed Durex surveys and flirting sites in different countries to find which destinations are full of cheaters and which are squeaky clean.
At the top of the unfaithful list was Thailand.
The Asian country was home to 56 percent of cases studied.
There are a number of theories to suggest why Thailand has claimed the top spot.
Some think it might be the spicy curry, which they say is aphrodisiac.
Sex tourism is also one of the country's biggest selling points.
Denmark was the second most unfaithful country in the global ranking.
Almost half (46 percent) of its citizens have been unfaithful, according to the research.
It was followed closely by Italy on 45 percent.
The exact same proportion of people deceived their partners in Germany too.
France came in fifth - a country where love and passion rule the roost - comprising 43 percent cheaters.
It appears the cold days in Norway have a remedy, with 41 percent having extramarital relations.
Belgium followed closely in its footsteps on 40 percent.
According to the magazine New Europe, the Belgian webpage of extramarital meetings 'Gleeden' had more than 1.1m users last summer.
Lower than its European friends but still sizeable was Spain, where 39 percent have cheated at least once.
Just when you thought the UK might have been left off the list, it makes an appearance.
Its landed the title of the ninth most unfaithful country on the planet, with 36 percent cheaters.
After the cyber attack on Ashley Madison - a website for extramarital meetings with more than 37 million subscribers - it was revealed that London was also the ninth most unfaithful city in the world.
The British capital held almost 180,000 accounts.
Rounding out the top 10 was Finland, where infidelity is not as taboo.
More than two thirds (36 percent) of Finns admit they've had an affair.