Patch up warmly this winter if you’re running Java. That’s the advice from .NET shop Microsoft, which reckons Oracle’s platform is the single biggest target for hackers.

Java proved the single most popular target in the 12-month period to the end of June, according to Microsoft’s latest Security Intelligence Report has found here (warning PDF).

Microsoft blogged about the findings here.

And hackers were targeting vulnerabilities that are not only several years old but are known about and have been patched by Java’s owner, Oracle.

The number-one exploit was CVE-2010-0840, affecting the Java Runtime Environment (JRE), disclosed in March 2010 and addressed with an Oracle update the same month.

Hacks on this hole surged tenfold in the first quarter of 2011 up from “a low level” in the fourth quarter of 2010.

The advice of Microsoft’s Trustworthy Computing director Tim Rains was simple: “If you haven’t updated Java in your environment recently, you should evaluate the current risks. Note: you might have multiple different versions of Java in use in your environment and should evaluate with this in mind."

He continued: “Keep all software in your environment up to date, not just Windows; assume attackers are targeting vulnerabilities in all prevalent software.

The JRE contained some of the most common exploits, he said. Vulnerabilities in the Java Virtual Machine (JVM) and Java Development Kit (JDK) for Java SE were also popular targets.

Between a third to a half of all exploits detected by Microsoft’s anti-malware were Java exploits – in every quarter in the year between Q3 2010 and Q2 this year. "Attackers have been aggressively targeting vulnerabilities in Java because it is so ubiquitous," Rains said. ®