Virus and/or malware warning when entering site

I work for an online travel and leisure company and a few days ago peopele
started calling us and saying we had a virus and/or malware , spyware warning
popping up when they tried to get into the site. The message is
below:...............

Reported Attack Site!

.......This web site at www.forcetravelclub.co.uk has been reported as an
attack site and has been blocked based on your security preference.


Attack sites try to install programs that steal private information, use
your computer to attack others, or damage your system.

Some attack sites intentionally distribute harmful software, but many are
compromised without the knowledge or permission of their owners. END......

Our IT guy has run all the usual virus and spam/maware/spyware programs and
they all come up clear. I was wondering if the reason for this may be that
someone has hacked into our server and/or done something which makes this
message come up. Also when you do a Google search for our site ( Force Travel
Club) you also get a warning that the site may harm your computer if you go
into it.

Its causing us loads of problems and everyone who goes near the site gets
these warnong messgaes and stay way clear. I would be very very grateful for
any help or advise on how to deal with this problem


Thanks in advance.

JC