Thanks for all the advice! I did take the snail out and get the algae off (without popping it) and wipe the snail's shell down with a napkin before putting it back into the aquarium. I really hope that did the trip. I definitely don't want any nuisances in my tank!
Since I had the snail for only a week, do you think the algae could've multiplied and spread during that time? I keep checking my rocks and substrate, and I don't see anything ...