Thanks for your information!
Maybe my information is misleading...The two freeware I mentioned not only work well with CF Cards but also other types of mass storage devices such as Harddisk, SD, MS, etc.
Furthermore, It is essential to wipe out the free space before disposal of your storage devices. You never know how the next person will treat your sensitive data. However, the procedure of wiping out the free space is indeed very slow......
For harddisk, degauss is a viable alternative solution....
Besides, I am finding similar tools in Mac version. Any brothers have good sugguestions??