A shortcoming in browsers including Firefox and Opera allows crooks to easily hide an entire malicious web page in a clickable link - ideal for fooling victims into handing over passwords and other sensitive info.
Usually, so-called "phishing attacks" rely on tricking marks into visiting websites designed by criminals to masquerade as banks and online stores, thus snaffling punters' credentials and bank account details when they try to use the bogus pages. However this requires finding somewhere to host the counterfeit sites, which are often quickly taken down by hosting companies and the authorities or blocked by filters.
Instead, the malicious web pages can be stored in data URIs - uniform resource identifiers, not to be confused with URLs - which stuff the web code into a handy string that when clicked on, instructs the browser to unpack the payload and present it as a page.
