Cheating is at it's peak in recent contests and I imagine it'll only increase in upcoming contests. As here on Codeforces, you are Problem Solvers, Please feel free to give absolute best solutions and reply about the bugs and shortcomings about other solutions in comments.
Let's see the Problem:
We have some sufficiently good coders who have created an Alt-Accounts. They are good as they are able to solve problems of some good enough difficulty (for eg: Problem E in recent 733 Div E contest). Now, of those good coders, we have some 'X' number of coders who with some modification (could be different language) make their solution in public (on Telegram or on their own websites which give them Ads money). These solutions made public are used by 'Y' users.
To make this thing become more difficult or stop increasing 'X' in future, I request MikeMirzayanov to please use some restrictions on who can create account. I have following restrictions in my mind.
1] Allow users to only create account using well known domain names (for eg: gmail, yahoo, outlook etc). This list should be updatable. Also, popular domain names specific to countries which I'm unaware of can be added.
2] All email-ids with
.edu should be allowed.
3] Users must use account twice in 40 days else account should be deactivated (not removed) and next time he / she logins, he must verify email again or (if exists, name 5 persons he have friended to) or must be above 1600 ratings.
4] Persons of shy nature like me make alt account to put their views. If there were some button by which I could post blog using my account anonymously i.e author of blog should be displayed as 'anonymous'. Then, I wouldn't be creating new account.
To catch 'Y' users, 1] For some problems with good enough computations, time limits and memory limits can be used judge a cheater. For example, in yesterdays problem 'E' notice this. Here we can (if possible) make MOSS to be more strict with solutions having similar time and space requirements.
2] Generally, only 10% participants tries to hack that too for max 20 minutes speaking generally. We can make 20 minutes post contests as hacking phase.
3] I imagine there exists some time period, where number of accepted solutions by users with less than 1400 rating for problem with greater than 1700 difficulty for example, increases a lot suddenly. All solutions within this time period must be judged using strict or more powerful MOSS. This is due to fact that those users get solutions at same time from cheaters on telegram or other source and everyone of their group receives the message at same time.
4] There exists some cheaters who are good, and hence we can encourage those users to supply code with trojan horse to those telegram.
That 'trojan horse' idea is too wicked and is too hard and impractical to implement. That probably violated telegram's rules. btw it's dangerous for those 'good' cheaters. Also, we can't rely on cheaters to boycott cheaters. I'm almost sure that this will backfire.
Depends on your definition of a 'trojan horse'. I could argue that many of the recent leaked cheater solutions had been already nicely trojan horsed (a lot of them contain some sort of very unique and easily identifiable wackiness). You can find more explanations and an example here: https://codeforces.com/blog/entry/8790?#comment-808194
Now most of the cheater accounts on codeforces have been contaminated by these 'trojan horses' and shouldn't be very difficult to identify. But would anyone be interested to do that? Olympic doping probes are stored for many years and then re-checked with more modern methods later. The codeforces plagiarism checker can be also improved and used to re-test the older contests data in the future.
By the way, anyone can download user submissions database from codeforces and implement their own independent plagiarism checker, recalculate user ratings (after cheaters removal) and host the recalculated ratings on some website. Again, would anyone be interested to do that?
Well I probably thought that 'trojan horse' meant the virus itself, but not the strange bits of code you insert to prevent instant copying. Still that's pretty much impractical because not all cheaters are dumb:(