There are some interesting articles on how to clear out the last login history, however, all of them offer the same result.  From several approaches, I have formulated a short and efficient one-liner.

The three files are /var/log/wtmp (successful login/logout) /var/log/btmp (bad login attempts) and /var/log/lastlog (last logged in). The are respectively accessible via the last, lastb, and lastlog commands.

This approach is offered by many sites.

echo > /var/log/wtmp
echo > /var/log/btmp
echo > /var/log/lastlog

From that I tried the following and this didn't work and produced an error /var/log/[bw]tmp: ambiguous redirect

> /var/log/[bw]tmp /var/log/lastlog

However, after trying a few things, I discovered the truncate command.  By using the -s switch and selecting the size of zero, we can achieve a working one-liner.

truncate /var/log/[wb]tmp /var/log/lastlog -s0

 

Source(s)
http://www.shellhacks.com/en/HowTo-Clear-or-Remove-Last-Login-History-in-Linux
http://www.cyberciti.biz/faq/howto-display-clear-last-login-information/
http://stackoverflow.com/questions/2423281/how-to-empty-truncate-a-file-on-linux-that-already-exists-and-is-protected-i