Skype is being used by hackers to spread a malicious 'worm' that infects Windows PCs and can lock users out of their machines.
Skype users are warned not to click on any messages or links that they do not recognise.%VIRTUAL-SkimlinksPromo%
The security threat comes in the form of a seemingly innocent instant message on Skype saying "lol is this your new profile pic?" When users click on the message they unwittingly download a file containing a Trojan horse malware file.
This Trojan horse opens a backdoor, allowing a remote hacker to take control of the infected PCs.
"Before you know it, your computer has been recruited into a botnet [security threats that spread via Facebook, Twitter and instant messengers] and could fall victim to a ransomware attack," explains a spokesperson for internet security specialist, Sophos.
Skype has not disclosed how many users are affected by the threat. It said in a statement: "Skype takes the user experience very seriously, particularly when it comes to security. We are aware of this malicious activity and are working quickly to mitigate its impact.
"We strongly recommend upgrading to the newest Skype version and applying updated security features on your computer.
"Additionally, following links - even when from your contacts - that look strange or are unexpected is not advisable."
Sophos warns that Skype users may be less in the habit of being suspicious about links sent to them than, say, Facebook users.
"Always remember to be suspicious of unsolicited out-of-character messages sent to you by your online friends," said a spokesperson.
"You don't know that it was a friend who sent you the message, all you know is that it was their account which posted it to you... and who knows if it was compromised or not?"
The top 10 scams of 2011
Skype users targeted in security threat
Land banking involves plots of land offered for sale, often online, with the promise of sizable returns when planning permission is approved for housing or other development. Yet often the land is located in areas protected from development by planning law.
The companies involved soon disappear with investors' money and as the firms are not protected by the Financial Services Authority, their funds are not covered by the Financial Services Compensation Scheme
It is reasonable to assume that if you take out a mobile phone contract at £30 a month for 24 months that's exactly what you'll pay unless you exceed the tariff. Yet mobile phone providers have come under fire for a snag buried in the small print – a clause to allow mid-contract price rises.
Prices are rising by a median of 81p a month and 70% of consumers are completely unaware off this sneaky move, according to Tesco Mobile, so be sure to check any new contracts before you sign the dotted line.
Fraudsters recruit unknowing accomplices through email under the guise of offering employment, seeking a personal favour, or through internet shopping sites. The recruits are persuaded into receiving what are essentially fraudulent payments and then passing funds on.
The 'mules' are frequently offered a small financial incentive to encourage involvement and face difficulties in proving their innocence when the fraud is discovered.
The scams claim to offer people the chance to profit from carbon credits. Under regulations that permit businesses to emit a tonne of CO2 – the companies claim to offer investment in green projects like a forestry scheme or a solar panel project, which generates carbon credits that are then sold on to heavy industry.
A flashy brochure or website tells of a reliable 'government-backed' scheme which provides reliable returns for investors. Such a scheme doesn't exist however – a reality investors only discovered when they have parted with their cash and the company is untraceable. As with land banking, fraudulent companies are not covered by the FSA so victims have no course for recompense
Receiving an email from the taxman saying you are owed a payment may seem like a nice surprise, but it is actually from fraudsters trying to relieve you of your cash instead.
The emails provide a "click-through link" to a cloned replica of the HMRC website. The recipient is then asked to provide their credit or debit card details - all the information the criminals need to clear your account, and sell on your personal details.
Insurer Direct Line reported a hike in the number of 'crash for cash' scams last year – where fraudsters fake accidents by making unnecessary emergency stops at busy roundabouts or slip roads, forcing motorists to crash into them.
They then make bogus claims to the innocent motorist's insurer, often including fictitious injuries and passengers.
Learner drivers have been taken for ride by being unknowingly taught by trainee instructors. An investigation by the AA found up to 27,000 extra driving tests have been failed in the last year because one in 10 learner drivers are unwittingly taught by an instructor they do not know is learning on the job.
July saw the arrest of a Leicester postman who stole £46,686 worth of mail over two-and-a-half years. Yogeshbhai Patel, 38, was jailed for two years for stealing mail including 2,000 DVDs and 2,250 games along with CDs and other electrical equipment. He intercepting the valuable packages and spent the money on living a luxury lifestyle including helicopter rides and a trip to Las Vegas.
The Trading Standards Institute reported over 200 cases where elderly homeowners have been targeted by telephone cold callers, purporting to be from their energy supplier and offering energy saving devices which could cut their bills by 40%.
The TSI tested the devices in homes where owners had fallen for the scam, only to find they both failed to satisfy electrical safety standards or deliver any tangible energy savings.
Thermal cameras that track ATM pin numbers are the latest weapon in their arsenal and US scientists have warned it is the next threat for this form of crime. Researchers at the University of California at San Diego found that up to 45 seconds after a person types their pin code into an ATM machine or door entry pad the numbers and even the sequence are still readable by thermal cameras.