We have recently received reports about a hacker who goes by the alias und3rm4t3r. He has been threatening innocent people for money and must be stopped. Help us find him and get us the flag.
I've found und3rm4t3r profile (https://twitter.com/und3rm4t3r/). One of the tweets seems interesting:
So, I've checked the wayback machine for a snapshot (https://web.archive.org/web/20200723112257/twitter.com/und3rm4t3r/) and found the flag :-)