On Sunday, Yahoo (YHOO) confirmed that some Yahoo websites may have transmitted malware infections to Yahoo users.
Yahoo said the malware infection occurred on Yahoo’s European websites, which were infected by malware contained in advertisements that appeared on the Yahoo webpages. The disclosure by Yahoo followed an announcement by a Dutch Internet security firm that revealed that some ads posed by ads.yahoo.com had been compromised with malware, Reuters notes.
The malware-infected ads were removed by Yahoo. Malware can be used to obtain data used in identity theft. The Dutch security firm said that the hackers responsible for infection Yahoo ads had not been identified. People who visited Yahoo websites in the United Kingdom, France and Romania were most vulnerable to the malware. As many as 27,000 computers that visited Yahoo European websites may have been infected by the malware each hour that they were posted.
Yahoo noted that the mobile devices and Apple’s (AAPL) Mac laptops and desktops were not vulnerable to the malware infection on the Yahoo websites in Europe.
Last month, Yahoo said that it was moving to fix technical problems that had disrupted service for some users of Yahoo Mail.
Despite news of the Yahoo malware breach, YHOO stock climbed more than 1% in Monday pre-market trading. YHOO stock has doubled since February 2013.