fcheck is a program that emails an alert when important files or directories change. This is useful for change control or detecting unauthorized modifications that may indicate an intrusion. The article covers also about some problems that might arise with that useful tool.
If you have accidentally deleted a file it can be recovered with Isof. The article describes a deletion and recovery of a file using Isof. (Article in Greek).
When a file is deleted in a filesystem, it is not removed from the disk, it's just marked and the data is still there. A secure tool to delete files is shred. It writes and rewrites many times on the disk to ensure that the data are really erased. (Article in Greek)