Sexy and sleek smartphones are on the horizon and the rush is on to sell that old handset as consumers try to recoup some cash that will add up to the fund for their next gadget buy.

Security experts, however, warned that mobile phone owners should first ensure that the handset they'll be giving up would not compromise their privacy, meaning the data in the unit will be no more for others access and tinker with.

And the best option available for the average consumer, according to Yahoo blog 'Upgrade Your Life', is to wipe out all traces of personal data from the phone via factory reset, a function that is offered on all mobile phones - from the once popular feature phones to the now ubiquitous smartphones.

Phone owners wary of unintentionally sharing their private lives with the next person fidgeting their gadget should be comforted by the fact that factory reset would normally eliminate all information from a mobile phone, the blog said.

That single phone function is its 'resurrection tool' as soon as the process has been completed, any unit would reassume its original state when it was first rolled out from the production line.

No phonebook, images and messages should remain once the factory reset button has been triggered and the wipe out operation concluded, Yahoo said.

But the process itself was fraught with a number of loopholes, according to computer forensic expert Steve Burgess.

The strength of security procedure wholly depends on the mobile platform that governs a specific unit, Mr Burgess warned.

And in this respect, Apple's iOS and Research in Motion appear to be on the top of the field.

Factory reset on any BlackBerry phones is robust enough that owners would simply apply the process and wait out for more than a month and they can be assured that all data will be lost forever, according to Mr Burgess.

The same goes with all iPhone editions, he added.

"With an iPhone, when you do a factory reset, it removes all of the encryption keys, which is the same as wiping it," the security analyst told Yahoo.

Data, however, that were once hosted by an iPhone could still be technically accessed if someone would be willing enough to spend a fortune in setting up a supercomputer, which is the only tool he knew would possess the juice for such efforts, plus the necessary skill and expertise of course.

Among the present platform there is, the weakest link would be Android, which incidentally is the dominant smartphone ecosystem, basing on data recently supplied by analytic firms.

Android's factory reset muscle could easily be overwhelmed by a determined hacker as the process itself only "masks the location of the data," that users meant to erase, Mr Burgess said.

And since many Android handsets were built with memory expansion capability, that added consumer attraction proved as the system's security Achilles heel.

Memory cards serve as natural gifts to data miners, Mr Burgess told Yahoo, since information buried deep on the storage device through numerous reformatting can still be retrieved by simply employing software that are easily available to hackers.

In comparison, Android phones are inferior when pitted to the most basic feature phone because the unit is simple enough that it can only hold too little data and likely not too much of a use to hackers.

Feature phones also usually use internal memory and in order to extract data from them, one would need proprietary cables to connect them to a PC, a feature that can be regarded as the device's inherent security firewall, Mr Burgess said.

In the end, apart from relying on the supplied security tools of mobile phone platforms, experts suggest that sellers exercise prudent and practical actions prior to actually parting ways with their old units.

The simplest acts would be taking out the SIM and memory card from a phone that is on its way out, then subjecting the device on factory reset procedure, moves that Mr Burgess said are the best privacy insurance in existence.