Activists with hacker skills were behind more than half the data stolen in cyber attacks last year, according to findings released on Thursday by Verizon Communications.

While criminal groups accounted for an overwhelmingly majority of cyber strikes on networks, "hacktivists" were the ones who rampantly looted data once inside computers, Verizon said in an annual Data Breach Investigations Report.

"This re-imagined and re-invigorated specter of 'hacktivism' rose to taunt organizations around the world," the US telecom titan said.

"Many, troubled by the shadowy nature of its origins and proclivity to embarrass victims, found this trend more frightening than other threats."

About 98 percent of computer network breaches at companies last year were the work of outsiders, with criminal groups out for profit were figured to be behind 83 percent of those attacks.

However, it was self-described activist organizations such as Anonymous and Lulz Security who stole 58 percent of the data while being involved in far fewer cyber attacks, according to Verizon.

"While good old-fashioned greed and avarice were still the prime movers, ideological dissent and schadenfreude took a more prominent role across the caseload," the report said.

The report cited data provided by the US Secret Service, the Dutch National High Tech Crime Unit, the Australian Federal Police, the Irish Reporting & Information Security Service and the Police Central e-Crime Unit of the London Metropolitan Police.

The Verizon findings were released on the same day that an IBM X-Force 2011 Trend and Risk report indicated that tightened security at companies is forcing cyber crooks to rethink tactics and shift to new fronts such as smartphones.

The X-Force report indicated hackers were increasingly resorting to automated password guessing programs, attacks on mobile gadgets, and "phishing" attacks that trick people into downloading viruses or revealing sensitive information.

"We've seen surprisingly good progress in the fight against computer crime through the IT industry's efforts to improve the quality of software," said X-Force threat intelligence and strategy manager Tom Cross.

"In response, criminals continue to evolve their techniques in an attempt to find new avenues into an organization."

Attack techniques include injected malicious code into legitimate websites or ruses that involve impersonating popular social networking services, X-Force warned.

In a bit of good news, the amount of spam email in 2011 was about half that in 2010, according to IBM.