Take a valid credit card number, such as
4111-1111-1111-1111, change it slightly, to
4111-2111-1111-1111, and it ceases to be valid. This is because the last digit of the number is a checksum calculated from the preceding digits via the Luhn algorithm. It’s not particularly clever; it’s not cryptographically secure. It’s not meant to be. What it’s intended to do is to protect against accidental data entry errors, and it does that very well.
When I saw this Daily Express front page online, I thought it must be a parody. It wasn’t until I saw a physical copy of the paper the next day that I really believed that they had actually printed something so inflammatory and xenophobic:
It may surprise many people, but Microsoft is fairly irrelevant to my daily life. I don’t use Microsoft Windows. In fact, no one in my office uses Windows. I don’t use Microsoft Office. At work, I have a Mac; at home, I run Linux.
I’m back from holiday, I’ve slept, and I’ve fixed the latest round of problems with the downloader.