Windows Security Center does not provide an antivirus. It is only an
alerter. What antivirus product do you have installed? Please give the
name and version of the program.
Depending on the av program, sometimes Security Center will report that
the av is out of date when the av just hasn't checked for virus
definition updates yet. However, this can also be symptomatic of
malware.
We just don't have enough information about your computer to give you
focused help. Refer to this link for what to include in a newsgroup
post:
