Researchers at Kaspersky Labs have found malware which, unusually, does not install any files on its victims PCs.

The researchers aren’t quite sure how unusual it is, describing it as both “unique” and “very rare”, but no matter how scarce this type of malware is it does sound rather nasty as it “… uses its payload to inject an encrypted dll from the web directly into the memory of the javaw.exe process.” That mode of operation means Windows and MacOS are both affected by the exploit, which is hard for many antivirus programs to spot given it runs within a trusted process.

Once under your machine’s guard, the malware tries to attack Windows User Account Control so it install the Lurk Trojan and connect to an associated botnet. That installation attempt is the malware’s key task, as living in RAM means fileless malware won’t survive a system reboot.

That the malware is able to do so is down to a known Java vulnerability, CVE-2011-3544 to be precise. Snoracle has long-since patched that hole. Another mitigating factor that will hopefully make this a short-lived attack is the fact Kaspersky picked it up in ads served only on Russian web sites. The security company has informed the ad-serving company and the offending code has been withdrawn.

But researcher Sergey Golavanov also warns “we cannot rule out that the same exploit and the same fileless bot will be used against people in other parts of the world: they can be distributed via similar banner or teaser networks in other countries. It is likely that other malware, not just Trojan-Spy.Win32.Lurk will be used in the process. that "we cannot rule out that the same exploit and the same fileless bot will be used against people in other parts of the world: they can be distributed via similar banner or teaser networks in other countries. It is likely that other malware, not just Trojan-Spy.Win32.Lurk will be used in the process.” ®