Law enforcement agencies can count a few recent victories against cybercriminals, but agents say the battle against them isn't getting any easier.

Highly organised cybercriminals are using increasingly sophisticated tools and methods that make them hard to trace, said Keith Mularski, supervisory special agent with the US Federal Bureau of Investigation's Cyber Division.

"They have evolved over the years," Mularkski said. "It really is organised crime."

Mularski, who spoke at the RSA conference in London on Wednesday, has had great success in infiltrating organised cybercrime rings. He successfully infiltrated a ring known as DarkMarket, an online forum where criminals bought and sold personal data, such as credit card numbers. DarkMarket was shut down about a year ago and 59 people were arrested, with the help of authorities in the UK, Germany, Turkey and other countries.

While the DarkMarket bust was a big win, there are still such forums operating today and they're hard to infiltrate. New members must be vetted for reliability and to ensure they're not FBI agents like Mularski.

The malicious software programs used to collect the data have become insidiously complicated and hard to detect. Financial organisations now are in a "raging battle" against "high-grade" weaponry, said Uri Rivner, RSA's head of new technologies for identity protection and verification, who gave a presentation earlier in the day at RSA.

Those programs go by names such as Sinowal -- also known as Mebroot and Torpig -- which is a nasty rootkit that burrows in a computer's master boot record below the OS. It may not even be removed by reinstalling the operating system. It can steal data and even modify the HTML of web pages requested by a user.

Computers that do not have up-to-date software patches are in particular danger. Hackers often set up websites or hack legitimate ones to perform what's called a "drive-by" download, which automatically exploits vulnerable software programs to infect a computer.

Microsoft has particular insight into the problem. Late last month, the company released its free Security Essentials antivirus software and so far it has been downloaded 3.5 million times, said Amy Barzdukas, Microsoft's general manager for Internet Explorer and Consumer Security, who also spoke at RSA.