IT Contractors must ensure they protect their equipment from constantly evolving Zeus attacks, one expert said.

Amit Klein, chief technology officer at Trusteer, said Zeus has the ability to intercept and modify any incoming or outgoing data or web pages from the computer it has infected.

He explained that this is how fraud is conducted nowadays, with increased sophistication and craftsmanship seen around the HTML injections.

"[These vary] from pretty straightforward and almost naïve patterns such as requesting additional information from the user [or] by injecting additional form fields to the bank's login HTML page, to fully fledged behind-the-scenes fraud," he explained.

This comes after Tony Neate, managing director of GetSafeOnline.org, warned web users that financial institutions would never ask for a username and password in an email. He added that the best thing for the recipients to do is to simply delete them.