Thanks to a new strain of Java-exploiting Trojan Caphaw (aka Shylock), security researchers have spotted a surge in attacks against online banking customers.

The malware has targeted customers in at least 24 financial institutions, including Bank of Scotland, Barclays Bank, First Direct, Santander Direkt Bank AG and Capital One Financial Corporation, according to security researchers at cloud security firm Zscaler. Caphaw (Shylock) is most active in the UK, Italy, Denmark and Turkey.

Caphaw appears to be spreading using a Java exploit from compromised websites as part of a drive-by download attack. However evidence for this theory remains circumstantial, as an advisory from Zscaler explains.

"At the time of research, we were unable to identify the initial infection vector," Mannon and fellow Zscaler researchers Sachin Deodhar explain in a blog post.

"We can tell that it is more than likely arriving as part of an exploit kit honing in on vulnerable versions of Java. The reason we suspect this is that the User-Agent for every single transaction that has come through our Behavioral Analysis (BA) solution has been: Mozilla/4.0 (Windows XP 5.1) Java/1.6.0_07."

Mannon added: "We suspect it is coming from a Java exploit on the version listed in the blog. Other vectors this threat has used in the past include Skype, social media, and email spam."