Major websites including the BBC, Newsweek, The New York Times, and MSN ran malicious online advertisements on Sunday that attacked users' computers, a campaign that one expert said was the largest seen in two years.
The websites weren't at fault. Instead, they are unwitting victims of malvertising, a scheme where cyber attackers upload harmful ads to online advertising companies, which are then distributed to top-tier publishers.
Tens of thousands of computers could have been exposed to the harmful advertisements on Sunday, which means some running vulnerable software may have been infected with malware or file-encrypting ransomware.
Some bad ads were still appearing on some websites including the BBC on Monday, said Jerome Segura, a senior security researcher with Malwarebytes, in a phone interview Tuesday.
