In the same week that tennis announced significant steps to combat doping, Andy Murray has admitted that he had been "naive" to think cheating was not going on.

The Scot had been among several top players critical of testers showing up at his home at 6am and questioning whether drug-taking could really be of benefit to a "skill-based sport" such as tennis.

Murray is now a leading advocate for increased anti-doping measures and, as tennis confirmed it is to adopt the athlete biological passport, he admits he got it wrong.

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"I think I would say I was probably a bit naive, not understanding how much that stuff goes on in sport," said Murray, who begins his title bid at the BNP Paribas Open today against Russian Evgeny Donskoy.

Murray said Lance Armstrong's admission that he had taken drugs in each of his seven Tour de France wins had influenced his thinking.

"It wasn't just Lance Armstrong, almost every cyclist who was involved in the Tour de France was doing that, it was a whole sport," he said. "I don't think we have a culture of it in tennis, but stuff can go on and to make sure that in your head, you're completely comfortable, you need to have everything in place and everything done properly so everyone can agree that tennis is doing everything we can.

"It's not to say you'll never get a person cheating because you get it in all sports. But when you hear about the sort of lengths people were going to, to not fail drugs tests, it was ridiculous, so obviously we had to do more. I think the biological passport is a good step, but there is still more to be done."

The ITF's announcement that tennis will adopt the biological passport was accompanied by a big increase in the anti-doping budget, which totalled $2 million in 2012. The Grand Slams, ATP and WTA Tours, which fund it along with the ITF, last week agreed to double their contributions.

Though the detail of how many players it will cover remains to be ironed out, the biological passport is considered a better way to catch cheats than simple blood and urine testing. Rather than testing for specific substances, a player's blood profile will effectively be on record. Any significant changes to the profile could indicate a player is doping, enabling more targeted testing to be carried out.

Typically, Murray has read up on the subject. "I guess they have baselines and all the different levels for things throughout your career and they can monitor whether they're fluctuating and look back at it in 10 years and see, oh, he may have been covering something up with this drug and that's why whatever levels they're testing for dropped or rose," he said.

"There are still grey areas. People not failing drugs tests doesn't necessarily mean they're not trying to cheat. Everyone's testosterone levels are different. I don't know exactly how they test it, but if my testosterone level is lower than yours and I take something and it boosts my testosterone, but it doesn't go above the level, is that cheating?

"It's not viewed as being cheating, but in my eyes that's wrong. I wouldn't do that. Some guys are taller and shorter, you can't change that, it should be that we play completely naturally, but we're never going to get that."

Tennis has been criticised for carrying out relatively few blood tests compared to other sports, with the ITF doing only 187 in 2012, only 64 of which were out-of- competition. Blood tests are more expensive than urine tests and it will be interesting to see if the ITF manages to lift its numbers enough to make the passport effective.

On the court in Indian Wells today, Murray begins his title quest having to face the aggressive game of Donskoy, the world No 83 from Russia, who is a protege of former world No 1 Marat Safin.

Having lost his first match here in each of the past two years, the Scot is taking nothing for granted, especially given that he has not played for six weeks, since his defeat by Novak Djokovic in the final of the Australian Open.

But he arrived in California on the back of three weeks' training in Florida and seems raring to go.

"Sometimes the first match is difficult, but I usually play well after a break," he said. "I just have to make sure I fight for every ball."