they can transfer easily from store plants to your clothing then transfer to your plants very easily and is the most common way to get them. once on your clothes they'll be able to travel anywhere you go. there are many methods for controling them and info is easily found so i won't get into that other than saying when this grow is done it's best to fully clean the room and i'd even go so far as repainting the walls.

when flowering, an easy and safe method of control is using your tank-type vacumn cleaner and sucking em off...webbing and all. during veg, it's pretty much your choice as you'll have plenty of time for rinsing.