Delete that ATO refund email unless you have $300 to blow on decryption

As many as 24,000 Australian-based PCs may have malware that exposes them to a new mass ransomware campaign which encrypts victims’ files until a $300 ransom is paid.

The scam is targeting Australians primarily via refund notification emails purportedly from the Australian Taxation Office, according to a new report from Microsoft detailing the rapid rise of malware it’s calling “Win32/Upatre”.

Microsoft’s count of Win32/Upatre across the globe rose from 48,262 in August to 884,884 by the end of October. Ninety-six per cent of infections have occurred on US-based PCs. However, Australia had the fourth largest incidence rate, accounting for 0.27 per cent – or roughly 24,000 infections – of the total, behind the UK and Canada.

While “Win32/Upatre” is a threat in its own right, the malware is a beachhead for hackers to install other malicious programs on a victim’s PC. According to Microsoft and other security vendors, it has recently been used to install a variant of the Zeus banking trojan. This in turn downloads Cryptolocker, ransomware that carries more severe consequences for victims than previous police-themed ransomware targeting Australians since it will actually encrypt victims' files rather than pester them by blocking access to the computer with by locking down the screen.

Ransomware is a class of malicious software that is used to demand payment from victims to restore access to files or functions. It has hit Australian business and consumers in two distinct variants over the past year.

Small business in particular have been impacted by targeted ransomware, where the attacker compromises the business’s PC and encrypts important files, withholding a key to decrypt the files until payments are made. Non-targeted ransomware, which usually carries a logo of local law enforcement, has typically locked the victim’s screen without encrypting their files, demanding payments of around $100. Both variants can cause pain, but the attack that encrypts files leaves the victim with little choice but to pay up – unless they have backed-up their data on hardware that is not on the same network.

According to security vendor Trend Micro, CryptoLocker demands a $300 fee to supply a decrypting tool. However, as other security vendors have noted, paying the ransom does not guarantee that the attacker will unlock the PC.

According to Microsoft, the downloader malware that leads to this ransomware has been distributed primarily in spam with email attachments titled “ATO_TAX.zip” and “ATO_TAX_.zip". Spam previously associated with this downloader malware have usually included a message claiming the recipient has a tax refund awaiting, and includes instructions to download, save and open documents contained in the ZIP file. However, Microsoft notes that it is also being distributed “via Java and PDF-related exploits”. In other words, the attackers could snare victims by tricking them to visit a booby-trapped website or just by opening a PDF document.

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Tags securityATOdecryptionmalware

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