Also Wednesday, Sony said it had discovered defective parts used in 1.6 million Bravia flat-panel televisions that could cause the televisions to melt.
The company is offering free repairs worldwide.
The Bravia defect is a blow to Sony’s struggling television business, which has long prided itself on quality while trying to keep up with lower-cost rivals.
In a statement Wednesday, Sony said it suspected that hackers had obtained log-in data from other Web sites or sources and used those to try to gain access to Sony accounts. Access was thought to have been gained to only a handful of accounts, and no credit card or other sensitive data was stolen, Sony said.
The hackers appear to have tried to log in to Sony’s networks between Friday and Monday, the company said. Because many Web users use the same names and passwords for many sites and services, about 93,000 combinations matched.
The company detected an unusual number of log-in attempts from particular Internet protocol addresses and decided to freeze the accounts involved. Sony has e-mailed account owners to notify them of a possible breach and to ask them to reset their passwords.
“We were able to move swiftly, and we believe very few accounts were actually accessed,” said Satoshi Fukuoka, a spokesman for Sony.
The company was stepping up its vigilance against similar attacks, Mr. Fukuoka said, but he also urged users to make a habit of changing their passwords frequently for Sony and other online services.
New trouble at Sony’s electronics and entertainment divisions adds to problems for the Japanese technology leader. Sony has been contending with heightened competition from nimbler rivals, as well as a punishingly strong yen that has eroded its competitive edge and profitability in important overseas markets.
Sony, the largest Japanese exporter of consumer electronics, had to halt work at six plants after the earthquake and tsunami that struck northeastern Japan in March. In July, Sony cut its forecast for annual profit 25 percent to 60 billion yen ($782 million), after sinking to a first-quarter loss of 15.5 billion yen.
The attack follows a large data breach starting in April that compromised data for more than 100 million online game and entertainment accounts, including credit card information, and forced Sony to shut down the PlayStation Network.
It took Sony more than two months to fully restore the network, and its slow handling of the breach led to widespread criticism of its online security.
The company has since promised to overhaul its Web defenses and created the position of chief information security officer. Sony said that the latest attacks — which targeted the PlayStation Network and other online services offering digital content — did not suggest a security weakness on its part.
Sony has been eager to expand its network offerings to combine its gadgets better with content from its movie, music and video game businesses. The PlayStation Network allows users to download video games onto Sony game consoles, while the Sony Entertainment Network offers music and movies for a range of Sony products, including its Bravia televisions, Xperia smartphones and Sony Tablets.
But in the online sphere, Sony has fallen behind Apple, whose iTunes and App Store services have helped increase sales of both content, like music and games, and gadgets, like iPhones and iPads. In June, Apple said there were 225 million registered iTunes and App Store accounts, compared with a combined 138 million accounts on Sony’s main online entertainment networks.
Meanwhile, the defective parts discovered in Sony’s televisions affect 1.6 million liquid-crystal-display units, the company said in a separate statement.
A defect in an inverter transformer used for LCD backlights could cause overheating, smoke and melting parts, it said.
The company said it would repair the Bravia sets worldwide, including 400,000 TVs in North America, 600,000 in Europe and 189,000 in Japan. It might also announce further repair programs for other markets, Sony said.
Sony, which has lost money on TVs for seven consecutive years, said in August that it was preparing to overhaul the business to reduce costs and compete better against rivals, including Samsung Electronics of South Korea, the market leader. A push into 3-D TVs, as well as Internet-ready models developed with Google, have failed to stem Sony’s slide in global market share, which stood at 11.7 percent in the second quarter of 2011, according to DisplaySearch.