High-profile leaks of financial data left more than 50 million accounts containing credit card information and, in some cases, confidential details at risk. Phishing attacks, targeted Trojan horses and Web-based exploits compromised millions of PCs to create centrally controlled networks known as bot nets.

While the further adoption of Windows XP Service Pack 2 likely reduced the total number of successful attacks--one study found that online users were better protecting themselves--Internet service providers and consumer-focused groups, such as digital rights advocates and privacy watchdogs, remained wary.

"Although we have made some strides in helping consumers protect themselves, the threats are growing broader and more dangerous, so the risk of failure can be that much more catastrophic," Tatiana Platt, chief trust officer for America Online, said earlier this month regarding the study.

In 2005, the familiar threats of worm epidemics largely subsided. Instead, attacks targeting vulnerabilities in client-side applications--such as Internet browsers and antivirus software--rose to prominence. Data on bot networks revealed that those centrally controlled networks of computers remained a large threat. And, attacks targeting the systems of specific people in government and industry have managed to sneak under the radar of security systems that have been honed to detect mass infections.

Likely the most significant trend in 2005 was the number of data breaches that have resulted in the loss of personal and financial information, attacks only revealed because of the requirements of the State of California's Security Breach Information Act of 2003 (S.B. 1386).

In February, data collection firm ChoicePoint revealed that criminals created fake businesses to get sensitive and financial information on 145,000 U.S. consumers. Bank of America disclosed later in the month that a backup tapes containing information on 1.2 million government credit-card holders had gone missing. Topping the year of revelations, Mastercard International told consumers that online attackers managed to compromise the database of a third-party credit-card processor, CardSystems Solutions, leaking 40 million accounts encompassing the four major types of credit cards.

Lax server security has been a key problem for many of the organizations that have lost information. One Web programming error resulted in the University of Southern California exposing approximately 280,000 records containing the personal details of people who applied to the school. Guidance Software revealed earlier this month that information on nearly 4,000 customers had been stolen by attackers that gained access to an improperly configured server.

The frequent breaches have fueled a debate over federal legislation, though consumer advocates maintain that the current incarnation of the law waters down more stringent state laws.

Consumers' computers became more secure and resilient to worms in 2005, underscoring that the user behind the keyboard remained the weakest link in the chain of security.

Worms and viruses only scored two medium-sized epidemics. The Zotob worm used a flaw in Microsoft Windows' Plug and Play functionality to spread among Windows 2000 PCs in August. Less then two weeks later, law enforcement authorities had arrested two men in Morocco and Turkey in connection with the worm. The latest variant of the Sober virus--which arrives as an attachment to messages claiming to be from the FBI, CIA or German law enforcement--also spread moderately. The message convinced a German computer user to turn himself, and his child pornography collection, into authorities.

However, the worm and virus attacks have declined from their heyday when the MSBlast, or Blaster, worm infected more than 25 million PCs. Instead, bot networks and targeted Trojan horses--which some industry media professionals have labeled 'spear phishing'--have become more of a threat.

Two major arrests of bot masters or bot herders--the people who control bot networks--have shed more light on the threat of compromised PCs. In October, Dutch prosecutors revealed that they had arrested three men responsible for compromising and controlling more than 1.5 million PCs. In November, U.S. federal authorities charged a 20-year-old California man with profiting from his control of some 400,000 PCs. While many security experts doubted that the arrests would significantly curtail the expansion and trade in bot nets, some have pointed to such arrests as one reason why worms have become less common since the Sasser epidemic.

While bots are a widespread threat, the more silent threat of singular attacks on companies and government organizations is less well understood. Attackers have focused on creating technology to keep attack tools stealthy, and rather than creating worms that propagate wildly, have instead targeted specific individuals within companies and government agencies. The attacks are being investigated by the U.S. under the name 'Titan Rain,' according to a September article in Time Magazine.

The vulnerability disclosure debate resurfaced in 2005, as some researchers became less enamored of the way software companies were responding to flaw reports.

When researchers from the U.K. planned to reveal details of flaws in products from database maker Sybase, the company responded with legal threats, which it dropped in April after negotiations. The incident that gained the most attention was Michael Lynn's disclosure of Cisco vulnerabilities at the annual Black Hat conference in July. The researcher for Internet Security Systems resigned from the company so he could present details of security flaws in Cisco's routers. The companies then filed suit against the researcher, but settled a day later. The incident has riled up security researchers, however, with some groups committing themselves to reproducing Lynn's research.

The debate is far from finished, however. A recent auction of a previously unknown flaw in Microsoft Excel on eBay, reignited the debate over what constitutes responsible disclosure. eBay shuttered the seller's attempt to auction the flaw.

The year also left the future of digital-rights management somewhat in doubt as well.

In October, security researchers revealed that media giant Sony BMG had been using poorly designed software that resembled surreptitious software commonly employed by online attackers to enforce copy protections. The software hid itself from users, could not easily be uninstalled, and had major security flaws that compromised the security of consumers' PCs. Digital-rights advocates took the media giant to task, and law firms filed more than 20 lawsuits, including a government action filed by the Attorney General for the State of Texas.

A proposed settlement for six cases filed in the Southern District of New York would prevent Sony BMG from distributing copy protected CDs for two years.