The Long First Second Glitch, commonly abbreviated as LFS, is a very famous glitch in the MS version of Chip's Challenge that is caused by a rollover in the timer software after 6,553.6 continuous seconds of play.
Chip's Challenge uses a continuous upward counter stored in a 16-bit unsigned integer to decrement the time limit. Each increment of this counter is 1/10 of a second, and the timer counts down whenever anything ending in zero other than zero itself is read. This will not reset until the current session of play ends; clock setting or the Fullsec patch will eliminate its effect on the time.
Since 65,535 is the highest number that can be stored by two bytes of data, the counter rolls back over to zero. As zero does not count, it takes until 10 for the next decrement, by which time 1.6 seconds have passed since 65,530. This delay results in Chip gaining an extra , possibly worth an extra second.
The rules on LFS scores are absolute - even if the extra  did not add another second or, if it did, the score one second underneath is reported instead, the scores are invalid.
When playing very long sessions, such as bold time seeking on Monster Lab or Blobnet, the use of Fullsec (in addition to saving a lot of time and hassle) will prevent the vastly unlikely but tremendously devastating possibility of the long second occurring on the exact same playing as the luck of the Irish.
It is important to realize that, despite the glitch's name, it can happen to any second when playing a level (the demonstration had it appear as the second one). The name is historical, and dates from a time when the glitch was not well understood. Anomalous high scores had been occasionally reported, but no one knew how to reproduce these results.
Claimed scores that have been determined to be LFS
- Lesson 2 - 91 (as seen at the bottom)
- Lesson 8 - 97
- Nightmare - 137
- Lobster Trap - 287
- Trust Me - 294
Other impossible scores, even beyond the reach of LFS
- Lesson 1 - 85 (LFS can add only three moves and the route is 83.0)