Google's Android operating system has serious security flaws, says a mobile security expert.

Riley Hassell, who says he discovered the security loophole in the popular OS, canceled an appearance at the annual Black Hat hacking conference in Las Vegas last week. Hassell and his colleague Shane Macaulay decided not to present their research at the conference, saying that criminals might use it to attack Android smartphones, Reuters reported.

"When you release a threat and there's no patch ready, then there is mayhem," said Hassell, who founded boutique security firm Privateer Labs. He said he and Macaulay had already informed Google about the software faults.

But Google declined Hassell's claim, saying Android security experts had discussed the issue with Hassell and they didn't believe that any such security problems occurred with Android.

"The identified bugs are not present in Android," said Google spokesman Jay Nancarrow.

Hassell and Macaulay were supposed to make a scheduled presentation at the annual hacking conference, where they were due to talk about "Hacking Androids for Profit."

Just a few minutes before their scheduled presentation, the pair discovered some of their work may have repeated previously published research -- which was another reason they called off their appearance, they said.

"This was a choice we made, to prevent an unacceptable window of risk to consumers worldwide and to guarantee credit where it was due," Hassell said in an interview.

Back in May, three research assistants at Ulm University in Germany discovered a serious security hole in Google's Android operating system for smartphones, which, they claimed, could affect 97 percent of Android users.

The researchers wrote in a blog that those people, using Android devices running versions 2.3.3 and below, might come under attack, when they are connected to unencrypted Wi-Fi networks. According to researchers, anyone else on that network could gain access to, modify or delete Android users' calendars, photos and contacts, CNNMoney reported.

Following the news, Google announced that a fix was already in place, and it would be rolled out globally soon.

Recently, a 10-year-old girl, who goes by the handle of CyFi, found that games on smartphones or tablets running on Apple or Android mobile software can be hacked into by tinkering with its clock settings.