Hit trace gives you the possibility to check which parts of the code were executed and which not. The method implemented in OllyDbg is rather straightforward. It sets INT3 breakpoint on every command within the specified region. When breakpoint executes, OllyDbg removes it and marks command as hit. As each trace breakpoint executes only once, this method is very fast.
When using hit trace, special care must be taken not to set breakpoint on data, or with high probability application will crash. For this reason, you must analyze code to enable corresponding menu options. I recommend that you select strict or heuristical procedure recognition. Fuzzy option is too error-tolerant and often finds non-existing procedures.
When you set trace breakpoint even on a single command within the module, OllyDbg allocates trace buffers of twice the size of code section.
Note that when you remove hit trace, you simultaneously remove forced run trace.
