I have found Gixen a safe and reliable eBay sniping tool. I have been using it for a few years and had no problems. It appears quite secure and I have suffered no security issues. Sniping is good and efficient. You can either use it as free software or pay a $6 annual fee which gives you the extra "Mirror" features. These extras features above the basis eBay sniping service are:
Gixen Mirror is a multi-server, fault-tolerant sniping service, unmatched by any other sniping service or sniping software. Your snipes are sent twice, from two different hosting locations.
No limit on number of snipes.
No ads in the logged-in area.
Contingency group bidding - first failed bid cancels all the others in a group.
New! Multi-win group bidding - define how many items you want to win in a group.
Wider choice of snipe time choices (3,6,8,10,12 and 15 seconds).
Auction end times refreshed hourly, as opposed to daily.
Other small perks provided to Mirror users only, such as CSV export / import.
It is the multi-server aspect that makes paying the extra $6 well worthwhile. With the snipe being sent from 2 locations I do not recall having a snipe not being made.
There is no need for extra software in your PC. There is also a plugin for Firefox which makes adding snipes a little easier.
I use it regularly and would recommend it as the best sniper I have found.