For several days, rumors circulated about a serious vulnerability in Intel processors. It wasn’t until January 3 that the official disclosure of the Meltdown and Spectre vulnerabilities was made, and it became clear how serious the problems were. To summarize, Meltdown and Spectre both allow malicious code to read memory that they would normally not have permission to.
Post from: Trendlabs Security Intelligence Blog - by Trend Micro
When Speculation Is Risky: Understanding Meltdown and Spectre