[UPDATE] Codeforces Cheater IOI Medalist

After reading MikeMirzayanov's blog, I decided to investigate TimDee again and found even more than I expected. (Previous blog about this issue)

Accounts that are likely his:

TimDee, TimaDegt, definitelynottimdee, IHatePaiu, AlinLoh420, RobertLoh420, PuriceLoh420.

Some of these were created after the previous blog, meaning he didn't feel any remorse.

Offenses that I found (ordered by date):

Codeforces Round 890 (Div. 2) supported by Constructor Institute (TimaDegt, possibly prvocislo)

This is likely a case of multiple people using one account. Looking at the submission times and the codes (especially headers) reveals that while submissions for problems D {217324769} and E1 {217299337} were written by TimaDegt, submissions for problems A {217296384}, B {217302862}, C {217292141}, and E2 {217351566} were likely written by prvocislo. Even though the account was participating out-of-contest, I think it should still abide the rules.

Codeforces Round 875 (Div. 1) and Codeforces Round 875 (Div. 2) (TimDee, TimaDegt, IHatePaiu)

This one is honestly pretty wild.

Most importantly, IHatePaiu ranked 3rd in the contest, which likely affected many participants.

TimDee and TimaDegt participated in the Div. 1, but they seem unrated. (If anyone knows the reason, please write in the comments.)

For problem 1831D - The BOSS Can Count Pairs, IHatePaiu {207622747} sent the exact same code as TimDee {207716387} and TimaDegt {207771011}.

For 1831E - Hyperregular Bracket Strings, IHatePaiu {207658220} sent the exact same code as TimDee {207716972}.

Also, TimaDegt has many similar submissions to the problem 1831E - Hyperregular Bracket Strings, but his accepted code is very different.

The last two submissions ({207772463}, {207772514}) are sent in the same minute, yet they are highly different. I don't know what he exactly did, but he likely had access to someone else's codes. (If you have any idea who it could be, please write in the comments.)

Codeforces Round 812 (Div. 2) (TimDee, IHatePaiu)

Codeforces Round 797 (Div. 3) (TimDee, IHatePaiu)

Codeforces Round 791 (Div. 2) (TimDee, IHatePaiu)

Codeforces Global Round 20 (TimDee, IHatePaiu)

I hope this will help Codeforces design a system to detect people using multiple accounts. Currently, it seems like doing plagiarism testing on skipped submissions and all submissions of a round if it is divided into multiple contests could be great solutions.

I apologize for any errors I could have made. If you have any suggestions or objections, feel free to write them in the comments. Additionally, if you would like to report a difficult cheating case or would like to help with exposing cheaters, feel free to DM me.