I've just fixed all the bugs in VOC which are related to Codeforces. Now you can use any problem from Codeforces problemset in your contests, and also you can add a complete Codeforces contest to a VOC contest. And the number of solved problems for each registered user is fixed, this number represents the number of solved problems during all contests, even if the user was unofficial participant, but solving problems as virtual participant doesn't count, and this problem should be listed in Codeforces problemset.