TOKYO — Sony said Wednesday that it had locked almost 100,000 user accounts on its PlayStation Network and other online services after detecting a spike in unauthorized log-in attempts. It was the latest in a series of online attacks on the company that have threatened to undermine user confidence in its Web-based offerings.

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.