Computer security researchers from ETH Zurich, Google, and IBM believe computer software would be more secure if, like a perishable food product, it were labeled with an expiration date. Only 59.1 percent of people use up-to-date, fully patched Web browsers, putting the remainder at risk from growing threats from diligent hackers, according to a new study published by the researchers in Switzerland.

The study is based on data archived by Google’s global search and web application servers between January 2007 and June 2008. It identified the number of web browsers worldwide with security loopholes. Computers running these browsers are vulnerable to unwanted downloads including spyware and viruses.

The researchers also concluded that as a group, Mozilla Firefox users were the most likely to be using the latest, most secure and stable version of the browser: 83.3 percent of Firefox users were found to have the latest version installed at any given time. That’s notably more than Web surfers using the latest versions of Safari (65.3 percent), and Opera (56.1 percent).