Someone given shell access can cause command-not-found to take up literally gigabytes of memory so that everything is swapped to disk and very slow. To see this in action, run the following in a terminal:
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ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: command-not-found 0.3ubuntu12
ProcVersionSignature: Ubuntu 3.13.0-24.47-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.1
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun May 18 09:09:07 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-02-09 (463 days ago)
InstallationMedia: Lubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.1)
PackageArchitecture: all
SourcePackage: command-not-found
UpgradeStatus: Upgraded to trusty on 2014-05-10 (8 days ago)
$ time <above long command>
real 0m42.187s
user 0m41.312s
sys 0m0.840s
$ top
24348(PID) xubuntu 20 0 1786796(VIRT) 1.695g(RES) 4032 R 100.0%(CPU) 29.2%(memory of 6GB) 0:05.04 command-not-fou
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