By Matthew Chapman BBC Radio Five Live

eBay is by far the world leader in online auctions

Criminals are obtaining the secret passwords of eBay subscribers and using their sites to conduct bogus auctions for non-existent goods.

In a growing number of cases, would-be buyers on the UK's most used website are paying thousands of pounds to apparently reputable sellers after winning auctions on the site, only to find out they had been dealing with criminals.

In an interview with Radio Five Live, eBay would not reveal exactly how many accounts had been hijacked.

"It is just not a number we give out as a business. We consider it to be business sensitive for various reasons," said Gareth Griffiths, head of trust and safety for eBay.

Sensitive issue

In one recent case up to 10 people are thought to have paid a total of £15,000 for non-existent hot tubs, while another would-be buyer thought he had purchased a £4,000 pound camper van which turned out not to exist.

It gets to the point where that is obstructive to our inquiry Ruth Taylor, North Yorkshire Trading Standards

In both cases eBay accounts had been hijacked to sell off the non existent goods.

The hijacking of sites is a particularly sensitive issue for the auction site, which relies to a large degree on the level of trust between the buyer and seller of goods for its success.

There are more than three million items for sale on the site at any one time.

Tools provided

EBay blames account holders for not installing proper security on their home computers and for replying to so called phishing e-mails.

The auction site says its users are often to blame for security breaches

These are fake e-mails made to look like official eBay messages and which demand the secret passwords to users' accounts.

Viruses are also said to be infecting home computers by installing themselves inside hard drives where they monitor the keystrokes of eBay users.

The viruses then make a record of secret passwords before sending them on to the fraudsters.

Describing it as an "off eBay issue", Mr Griffiths said "we have told people again and again".

"It is nothing really to do with us. We provide you with tools to help yourself."

When asked whether eBay's own computer could have been compromised, Mr Griffiths insisted that eBay's "systems are completely robust".

In both cases examined by the BBC, the eBay users who had their accounts hijacked claimed to be computer literate and vehemently denied that they had replied to phishing e-mails.

"There is no way I would have done that," said Dr Oliver Sutcliffe, a biochemist from Nottingham.

His site was hijacked over the space of one weekend to sell thousands of pounds' worth of electrical goods.

Obstructive delays

EBay is also under fire from law enforcement officials and manufacturers over levels of crime on the site and the levels of cooperation they receive.

Many big brands are far from happy with eBay's response

Trading standards officers who regularly investigate crimes perpetrated on the site have accused eBay of being "obstructive" in the way it responds to requests for information.

North Yorkshire Trading Standards says eBay can take up to two months to provide the names and addresses of suspects it is pursuing.

"If it takes up to two months then it is eating into a lot of time that we have to make prosecutions," said Ruth Taylor who heads the authority's special investigations unit.

"It gets to the point where that is obstructive to our inquiry."

Satisfaction level

Concerns have also been raised about the large amount of counterfeit goods on sale on eBay.

Adidas told the BBC that it monitored up to 12,000 auctions involving its goods every day on the British site, yet it estimated that up to 40% of all Adidas products available were counterfeit.

EBay says it has a special relationship with brand owners who can notify the site of auctions involving counterfeit goods, which will then be taken down within hours.

However, the Ben Sherman clothing brand says it recently took eBay five days to take down an auction of counterfeit clothing by which time much of it had been sold.

"I think one must say that it's highly unsatisfactory," said Barry Ditchfield, Ben Sherman's brand protection manager.

"With all the amount of profits that eBay makes, then there is ample scope for additional staff.

"Frankly, it is totally unsatisfactory, not just for Ben Sherman but for all brand holders."

EBay rejected the accusations, saying that the company had a good relationship with law enforcement officials.

"The satisfaction level is generally very high," said Mr Griffiths.

"Generally speaking, we provide a good service that people are pretty happy with."