Giving perk your SSN

So, I finally got the request for tax info and trying to read up on what people think about giving perk their SSN.

It seems that most people are OK with it, however plenty of people are advising not to trust them. I would hate to stop using Perk during this holiday season, as reward points are always easier to earn now than after the season. Is there a safer way to give it to them? They have a snail-mail address to send a hard copy to in case the webform isn't your cup of tea- is that better/safer, or ultimately is it just as bad as putting it on their online form? Can't tell if there are just some paranoid folks around here, or if it really is that scary.