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Ireland will kick off their Six Nations defence against England in Dublin this weekend.
Schmidt says he "stumbled" on spying missions by opposing teams but he would not reveal which team or teams he believed were involved.
"It's happened a couple of times," he said.
"I think when it filters back you are disappointed but you kind of acknowledge, 'OK, it's their process. It's their way of collecting information'. You just shrug your shoulders.
"But I don't think you can get distracted by it. And in the end I think if you became paranoid about it you'd never actually train properly.
"You'd always be worried by somebody looking. We always say, 'If they spy on us but we do it well enough maybe we'll still be able to get a result'."
England's coach Eddie Jones has recently admitted he spied on rivals but claimed he had quit doing it a long time ago.
Jones said: "Fifteen years ago, we used to send people out in costumes to watch training – it used to be part of the pre-match brief then.
"I can remember sending a coach who is now in a very senior position dressed like a swagman to watch one team train and he got chased out of there.
"You do not need to do it now because you see everything now in a game. I have been coaching for 20 years and it has always been going on. We don't see the value of it because we can glean most of the stuff from games now."
Sport espionage is the topic of the day in Britain, with Leeds United football manager Marcel Bielsa admitting he spied on opposing teams' trainings.
The Argentinian said last week that he has spied on every Championship opponent this season, and he even gave media a power point presentation.
"What I have done is not illegal," he said.
"It's not specified and it's not restrained. We can discuss about it. It's not seen as a good thing but it is not a violation of the law."
The England and Ireland rugby teams have been training near each other in Portugal and Jones has joked he is about to purchase some binoculars. But the matter is no joke to Schmidt.
Ireland are reportedly among teams who no longer conduct the traditional captain's run at stadiums the day before away matches.