Spanish insecurity experts from Informatica64 used a JavaScript Trojan horse to steal information from spammers and scammers, which is a bit like giving AIDS back to monkeys. In a presentation at the Black Hat security conference, security consultant Chema Alonso showed off a somewhat dodgy method to snoop on some very questionable people online.

The pair replaced cached JavaScript with an attacker's copy and used this to inject the JavaScript file into a victim's browser. Alonso set up an anonymous proxy server and then published its Internet address on a proxy forum. Within a day, more than 4,000 computers had connected to the proxy server and had the poisoned JavaScript file in their browser caches.

According to Dark Reading, Alonso found a variety of low-level criminals using their proxy server. There were fraudsters posing as British immigration officials offering work permits, a bloke pretending to be a pretty woman on a number of dating sites to con victims into sending money for a plane ticket there was another fraud involving flogging non-existent Yorkshire Terriers. By replacing one of the JavaScript files with a malicious version via the proxy server, the attacker can tailor attacks for a specific site, he told the conference.

He thought that it was likely that companies and governments are already using this technique to eavesdrop on criminal activity. He said that he could collect that amount of data in only one day doing nothing with two small JavaScript files. He thought it was too easy for governments and spooks to do the same thing.

The only way for people to sure that they are safe is that they use servers that they trust. In addition, privacy-sensitive people should regularly clear the browser cache.