Could I broke my SD card with badblocks or dd?

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https://bbs.archlinux.org – It was in some old phone of mine and appears to be as clean as brand new. But sudo dcfldd if=/dev/urandom of=/dev/mmcblk0 bs=4M count=1 gave 1+0 records in1+0 records out as an output so I actually can write into it, right? I played a little with the lock label but it's acting the same. If lock label is set to protect the data, the output is dcfldd:/dev/mmcblk0: Read-only file system so it's not the problem. I want to buy new card anyway but I just want to be sure that I will not broke it too. ;-)I've found this:The SD/SDHC/SDXC memory cards have a "Protected Area" on (HowTos)