system
Given the following post, respond as if you're commenting on Reddit:
human
[X-Men] In the X1 movie, how did Magneto know of Rogue and her abilities?

Rogue runs away from home and meets Wolverine and then the two of them are attacked presumably because Magneto can use her ability to power his machine. 

But how did Magneto know who she was or what she could do? 

Furthermore, how did the X-men know Sabretooth was attacking them at that time and place and save them?
gpt
Short answer, Mystique. She infiltrated the mansion and learned of Rouge's powers.

Long answer: Magneto and Xavier may have had a falling out after the events of X-Men First Classes, but they've tried to rebuild their relationship. This is apparent during a flashback in X3 when they visited Jean Grey together.

While their relationship never fully rekindled, they kept in-touch but also kept tabs, being frenemies and all. Max knew the academy would attract mutants with different powers and backgrounds, including those he could exploit. This would also explain why Mystique was at the academy in secret despite having close personal history with Charles.