It is safe, it has all happened to us on more than one occasion, then expose a list of ptc to which I belonged and that disappeared along with my work and earnings:
http://www.sambux.com/
http://www.solarbux.com/
http://www.bux-universe.com/
http://www.certbux.com/
http://www.ptc4ever.com/
http://www.unratedbux.com/
http://jssbux.com/account
http://www.standart-clix.com/
http://www.intlinx.com/
http://www.tatabux.com/pages/
http://www.onpaybux.com/
http://www.diesel-clix.com/
http://www.topstarbux.com/
http://www.morepaybux.com/
http://www.phd-clix.com/
http://www.intexbux.com/
http://www.hoolbux.com/
http://www.sekbux.com/
http://www.yimbux.net/
http://www.klickbux.com/
It is not a complete list, Possibly some of you list is longer.
Even I keep trying